Trinity River Watershed: Animal Spotlight

Benthic Macroinvertebrates

What are they and why are they important to river ecology?

Benthic: bottom-dwelling

Macro: see with the naked eye

Invertebrates: animals without backbones

Most of the life in rivers on any given day of the year are the small creatures that live out of the direct force of the river’s current, either attached to the rocks or wood, in spaces underneath or between pieces of gravel, or burrowed into silt. These animals include mussels, snails, worms, crayfish, and aquatic mites. But among all types of aquatic invertebrates, one class of animals stands out as the most diverse and complex – the insects.

An important term in river ecology is “benthic macroinvertebrate”, which refers to bottom-dwelling (benthic) animals without backbones (invertebrates), that you can see with the naked eye (macro). Ask a fly fisherman what trout and steelhead eat, and they’ll probably tell you salmon eggs if they’re available, sometimes other fish, occasionally snails, worms, grasshoppers or ants that fall into the stream, and with most frequency aquatic insects. Aquatic plants and algae photosynthesize energy from the sun. These plants then feed aquatic insect which in turn become an important energy for fish. Many insects have specialized mouthparts and behaviors to scrape algae and diatoms from rocks. Others feed themselves by shredding detritus (organic material that collects in rivers), or by straining food particles from the river’s flow, or by attacking and consuming other invertebrates.

Salmonid lifecycle and feeding


The mouths of small salmon fry are very small, and when their nutrient sac is no longer providing food prime food sources are plankton such as Daphnia (which could be considered “micro” invertebrates), small insect larvae such as chironomids (better known by their common names as midges or gnats) and young mayfly larvae such as baetids (known by fly fishermen as “blue-winged olives”).

Above, a chironomid larvae. Small and soft bodied, with generations as short as three weeks, this family of invertebrates rapidly colonizes seasonally flooded areas and provides excellent food for salmon and steelhead fry, as well as larger fish.
A larval giant salmonfly
These insects live for three years in the river before metamorphosing into adults. While growing, they mainly eat detritus (organic material that collects on the bottom of the river). Image credit:

An adult giant salmonfly (Pteronarcys californica)
A large stonefly that inhabits the Trinity River. On the Trinity River, these insects ‘hatch’, or metamorphize into adults in the spring. Image credit:

Older fish, the size of trout or steelhead, readily eat the larvae of larger insects such as caddisflies and salmonflies. Most aquatic insects are very small when they hatch from their eggs, and grow into progressively larger individuals after shedding their exoskeletons – a process called ‘molting’. Each growth stage is called an ‘instar’, and as they grow, each instar provides different sizes of food for different sizes of fish. After a range from a few weeks (for chironomids) to a few years (for some stoneflies and caddisflies) the insect pupates (similar to a caterpillar in a cocoon) and metamorphoses into a winged adult. Most of these adults are short-lived. Mayflies and stoneflies, for example, don’t even have functional digestive systems. They only live long enough to mate and deposit eggs in suitable locations along a stream.

A larval October caddis with a case made of stones glued together. While larger fish may eat these insects case and all, the high proportion of inedible material deters predators from eating them. October caddis generally spend two years in the river before they metamorphose into adults. They graze on algae and diatoms that cover rocks, but may also be observed feeding on dead salmon. Photo Credit:
An adult October caddis (Dicosmoecus spp), a large caddisfly that lives in the Trinity River. As their name suggests, these caddisflies metamorphose into adults in the fall, when they lay the eggs for the next generation. Photo credit:
A larval baetid (blue-winged olive) mayfly. Although this photo was taken in Montana, similar species inhabit the Trinity River. Baetids are generally multi-voltine (have multiple life cycles per year), and this, coupled with their small size, makes them ideal food for salmon and steelhead fry. There are over 1,000 species of Baetids worldwide, and they have a variety of feeding habits, but are generally good swimmers and move around the river bottom feeding on that algae and diatoms that grow on rocks. Photo Credit: Encyclopedia of Life
A male Baetis (blue-winged olive) mayfly. Baetid mayflies are common in dam-regulated river reaches. These mayflies can hatch spring through fall, and even sometimes in the winter.
Photo credit:

Macroinvertebrates and stream health

Many aquatic insects have very specific requirements for water parameters such as maximum temperatures, minimum dissolved oxygen, turbidity, pH, and salinity. These requirements make benthic macroinvertebrates very good bioindicators of stream conditions. The orders Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) are famous for requiring cold and clean water to thrive. In contrast, Chironomids, which belong to the order Diptera along with common houseflies, vary in their requirements depending on the species.

Stream ecologists can collect a sample of benthic macroinvertebrates and identify the species in the sample. In turn, the insects captured can then tell them about the condition of the stream. For example, if the sample contains a high proportion of individuals in the orders Ephemeroptera, Plecoptera, and Trichoptera, this indicates that the water quality is high. If the sample contains mostly species that live out their life cycle in just a few months, such as many species of Baetis and Chironomidae, this indicates that the water quality may change significantly between seasons. If the sample contains many species that have multi-year life cycles, such as salmonflies and October caddis, this indicates that water quality remains high throughout the year on a consistent basis.

The next time you visit the Trinity River, look around for aquatic macroinvertebrates. You might see cased caddisflies clinging to small cobbles. Turn one over, and you are likely to see mayfly larvae clinging to the bottoms. Look for the shed exoskeletons of stonefly pupa on branches and stems near the water’s edge. Look further to see if you can observe a trout or steelhead sipping adult insects off the surface as they lay eggs and complete their cycle of life.

James Lee, MS – Implementation Branch Chief

James Lee grew up near Redding, Ca, but his heart has always been in The Trinitys, where he chased tadpoles, salmon, deer, and gold nuggets for much of his youth. This love of the outdoors turned into an interest in managing fish, wildlife, water, timber, and other natural resources. 

Trinity River: Current Conditions

Trinity River: Current Conditions

Concerning news of spring chinook infected with an undiagnosed gill infection have been reported at higher rates than years prior and has the attention of agencies, anglers and those on the river. Although the average rates and the location of these reports have been concerning, some daily rates of reported infections have been alarming and have definitely garnered the attention of regulatory agencies. The evidence of disease is somewhat surprising because upper river temperatures are not exceptionally high. A key differentiating factor hypothesized by fish biologists, may be that the heavy sediment and ash loads from thunderstorms in June may have damaged the gills of the spring chinook that were making their way upriver at that time, stressing them and thus making them vulnerable to disease.

It is helpful to know that there are several advisory groups that meet regularly to discuss Trinity & Klamath River conditions. The KFHAT (Klamath Fish Health Assessment Team) evaluates current conditions and meets weekly and/or as needed throughout the summer and fall period.  The Klamath Flow Augmentations Releases (FARs) group meets bi-weekly (or as needed) and are meant to protect migrating salmon in the summer and fall months, when conditions can become poor in the lower Klamath River. The flows, water temperature, fish observations, and disease rates are all monitored using data collected by several partnering agencies such as the California Department of Fish and Wildlife (CDFW), Hoopa Valley Tribe and Yurok Tribe to determine if a FAR recommendation is needed.

Fish can catch disease if they are stressed and there are several factors that play into this (water quality: including turbidity and temperature, lamprey predation, being handled or caught, etc.). Experts are in agreement that water temperatures at Lewiston are good, around 53 F, which is about 3-4 F cooler than last year. Overall, water temperatures and flows in the upper Trinity River appear suitable for adults and would not be expected to cause gill lesions alone.

To monitor temperatures, there are currently four locations that upload to the USGS website located at Lewiston Dam, Douglas City*, North Fork Trinity River, and in Hoopa. You can view all of these temperature readings by clicking the corresponding links below. The links will also show last year’s (2022) temperature readings for contrast. We see river temps rise this time of year and should start to see them fall slowly down as day lengths shorten – typically starting in August. 

Those involved will continue to discuss any appropriate recommendations for responses to this issue, should a response be warranted. They will continue to monitor the situation and meet to discuss new information in the coming days.

*The Douglas City temperature gauge is now functioning. A replacement from USGS was administered and real time temperature readings came back on-line the morning of July 18. While the gauge that uploads to the internet in real time was damaged, data was still being collected at this site.

Featured Article – July

Lightning strike in the Trinity Alps Wilderness during a set of summer thunderstorms in 2023. [Photo credit: Anonymous]

Sediment and Summer Thunderstorms

Thunderstorms and sudden cloudbursts are common in the mountains during the summer. Following a wildfire, they can have dramatic results, especially after a dry year without significant rainfall. A single downpour can set a mountain stream roaring, sending a puff of suspended sediment downstream to wash into the river below. Usually this passes quickly, leaving little trace. Significant rainfall and subsequent runoff normally occur in fall or winter. However, an unexpectedly intense storm directly following a wildfire in 2022 lead to a natural disaster on the Klamath River. In August, heavy rain flooded an area burned by the McKinney fire, California’s largest wildfire that started in July that same summer, resulting in an enormous plume of sludge and debris that killed thousands of fish.1

Sediment is usually mobilized by the large storm systems that come in fall and winter during the rainy season, but a burned landscape is much more vulnerable. Wildfires cause loss of canopy vegetation as well as changes to soil properties. Storms can result in more water flowing over the land, leading to flooding and erosion, while delivering sediment, ash, pollutants, and debris to surface water.2 All that mobilized debris can choke small creeks and block local drainages, turning rivers into muddy, churning maelstroms.  And even after the water clears, the excess fine sediment can fill in pore spaces between cobbles where fish lay their eggs (redds), suffocating eggs and aquatic larvae on the bottom; it can also clog and abrade the gills of mature fish.3 

While erosion is a natural process, its effects on rivers and streams are highly variable, and the increasing frequency and intensity of wildfires is changing that dynamic.  Ongoing research by agencies like the U.S. Geological Survey is shedding new light on wildfire’s impact on soil and water.

Soil properties can change dramatically due to fire. For example, metals can be volatilized and rained down or deposited by ash, and the structures that burn can introduce all sorts of other materials into the mix. Each watershed reacts uniquely to wildfire. Topography, including slope, affects how much erosion occurs. The type of vegetation (or structures) burned and what was in the soil itself affect what ends up in the surface water. And the mechanics of the fire, like how hot the fire burned and how much of the watershed burned, affect what is in the runoff.4

When rains hit, the tremendous amounts of ash and sediment that wash into rivers and reservoirs cause physical disruptions. In addition to the large-scale runoff (landslides and debris flows), smaller-scale runoff increases the amount of fine sediment suspended in water. Sedimentation also decreases the water quality itself by changing the amount and type of dissolved organic matter (DOM). Fire releases nitrogen stored in plants and trees. Geochemists have also found that different trees release different metals, in different concentrations, when burned. For example, when a ponderosa pine burns it releases whatever metals it has absorbed from the soil and air, like iron and manganese. An aspen or spruce might emit more vanadium, lead, magnesium, or copper.5

Salmon redds are most vulnerable during and after spawning season, which starts in October. The first big storm in the Trinity Alps came in October of 2022. Deadwood Creek and Dutch Creek, tributaries to the Trinity River, dumped a ton of sediment into the mainstem that had failed to mobilize in the previous drought years. Deadwood Creek sits high up in the managed river system where some of the heaviest spawning takes place.  At the time of the storm, the Trinity River itself was still at baseflow (300 cubic feet per second), so it did not have the momentum to carry the sediment very far and it settled closer to the mouth of the creek, smothering a number of redds.

The solution? Once the eggs have hatched out in the spring, most fish can usually swim away from pulse-disturbances and pollution as long as their movements are not restricted by barriers like road crossings, dams and culverts.  TRRP is helping fund watershed projects that limit the sources of excess sediment and remove barriers to migration to give fish more ability to escape difficult conditions. These include the Supply Creek Berm removal project and the Carr Fire Recovery & Sediment Reduction Project, as well as the planned Oregon Gulch Culvert Replacement and East Branch East Weaver Creek Migration Barrier Removal.6 A proposal to synchronize winter storm events with flows out of the dam would help keep tributary sediment from piling up at creek mouths during storm events. The TRRP is also looking to support more projects that emphasize fire resiliency. Restoring the river and its watershed is the ongoing mission of the TRRP.

Trinity River Watershed : Plant Spotlight – July

California hazel (Corylus cornuta subsp. californica)

California hazel is a native shrub that grows in the moist shade of forest understory and riparian areas. The leaves are soft and fuzzy, and fall off during the winter (deciduous). During the winter months, the plants produce male flowers, called catkins, along with quaint red female flowers on the same plant. Once pollinated, the female flowers will very slowly develop into a pair of seeds. The seed husks are extremely bristly (like fiberglass) and have long beaks to them, giving this plant one of its common names, “beaked hazelnut”.

Hazelnuts don’t ripen until the later summer/early fall, and often, just one (or none) of each pair will make it all the way to maturity. Hazelnuts are tantalizing food stuffs for an assortment of critters, from insects, to small rodents, to birds, to large mammals. Humans are no exception – native hazelnuts roasted on the woodstove make a delicious winter treat. To harvest, however, we humans have to use our wit to outcompete the hungry critters, who will devotedly devour every hazel in sight if given the opportunity.

The historical relationship between humans and hazels is much more multi-faceted than mere consumption. Native Americans who share a range with this plant, including the Hupa, Yurok, Wintu and Chimiariko tribes have long utilized hazels in basketry and fiber-making. In the Hupa language, there is a different word for each of these applications. K’ila:jonde’ translates to ‘hazel’ or ‘hazelnut’, while tł’ohsch’il’e:n means ‘hazel brush switches’ or ‘hazel bush’. If separated from the plant, a hazel stick itself is referred to as miq’ik’itł’oy’, and the verb for twisting a hazel withe to make it flexible is k’iq’e:n.

California hazels are just one of the important characters that constitute our local flora; healthy ecosystems are comprised of a great diversity of native plant species. Stay tuned to learn more about local native plants and their ecological roles!

Photo top left: A hazelnut growing on the shrub. An unfertilized/undeveloped hazelnut is seen on the left.

Photo top middle: This old, twisted hazel branch would not be suitable for basket making.

Photo top right: An unripe hazelnut has been knocked onto the ground, but amazingly has not been consumed yet.

Photo bottom left: An immature hazelnut that has been foraged by local wildlife.

Photo bottom right: Ripe hazelnuts.

Veronica Yates, Riparian Ecologist

Hoopa Valley Tribal Fisheries Department, Weaverville

2023 Watershed Grantees

On June 16, The Bureau of Reclamation and the U.S. Department of Agriculture Natural Resources Conservation Service announced 11 projects totaling $6 million to be awarded as part of three Klamath Basin Salmon Restoration grant programs and 4 of the 11 aforementioned projects will be administered in the Trinity River watershed. The 4 projects selected will improve aquatic habitat by reducing fine sediment delivery, improving fish passage, and pursuing increases to tributary flows in the dry season in tributaries of the Trinity River. We congratulate the grantees and are excited to see the outcome of each project. Please read below to learn about each grantee, proposal and award amounts. To find the full Klamath 2023 Grant Slate from the NFWF website, please click here.

A photo of Deadwood Creek after the Carr Fire.

Deadwood Creek Sediment Reduction Project (CA)
Grantee: Northwest California Resource Conservation &
Development Council
Grant Amount:. . . . . . . . . . . . . . . . . . . $98,900
Matching Funds:. . . . . . . . . . . . . . . . . . $5,800
Total Project Amount:. . . . . . . . . . . . $104,700

Prevent sediment delivery to Deadwood Creek, a major
tributary to the Trinity River, to improve anadromous
salmonid habitat. The project will remove legacy mine tailings from Mill Gulch, decommission Thorne Gulch Road, install and enhance 12 rolling or critical dips, remove abandoned vehicles and debris from stream channels and floodplains, install a gate to prevent further damage and build stream enhancement features in Thorne Gulch.

Photo: Deadwood Creek after the Carr Fire in 2018. (TRRP)

Douglas City Community Services District Feasibility
Study for Fish Habitat Improvement in Trinity River
Tributaries (CA)

Grantee: Watershed Research and Training Center
Grant Amount:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . $78,800
Matching Funds:. . . . . . . . . . . . . . . . . . . . . . . . . . . . $5,600
Total Project Amount:. . . . . . . . . . . . . . . . . . . . . $84,400

Assess the economic feasibility of creating and maintaining a community services district (CSD) to provide a stable water supply to residents in rural Douglas City (Trinity County, California) to leave water instream for improved habitat connectivity for steelhead, coho and Chinook salmon in Browns and Reading creeks, tributaries to the Trinity River. The project would assist in determining if a CSD is an economically viable option to achieve environmental and community benefits under an increasingly dry climate.

Map provided by Watershed Research and Training Center.

East Weaver Creek Dam Removal and Intake Relocation
Phase II (CA)

Grantee: Northwest California Resource Conservation &
Development Council
Grant Amount:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . $120,600
Matching Funds:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $0
Total Project Amount:. . . . . . . . . . . . . . . . . . . . . $120,600

Remove a complete barrier to aquatic species including the threatened Southern Oregon/Northern California Coast coho salmon and restore fish passage to approximately 2.5 miles of cold-water habitat. The project will enable upstream fish migration for all life stages of all fish species in East Weaver Creek, tributary to the Trinity River.

Photo of the East Weaver Creek Dam provided by Northwest California Resource Conservation &
Development Council.

Indian Creek Fish Passage Barrier Removal Feasibility
Project (CA)

Grantee: Yurok Tribe
Grant Amount:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . $184,800
Matching Funds:. . . . . . . . . . . . . . . . . . . . . . . . . . . . $11,000

Total Project Amount:. . . . . . . . . . . . . . . . . . . . . $195,800
Evaluate conditions that create a barrier to anadromous
fish passage throughout a reach of Indian Creek, a tributary to the Trinity River, with a constriction point in the Indian Creek valley. The project will create a shovel-ready project to remove a significant barrier to fish passage and reopen 7.5 miles of stream and 85 acres of habitat suitable for threatened Southern Oregon/Northern California coast coho salmon, among other aquatic species.

Photo of the Indian Creek restoration area provided by the Yurok Tribe.