Water quality standards in the Spokane River are designed to protect redband trout, a subspecies of rainbow trout.
I’ve often wondered why we have low populations of our local redband trout in our river. Most metrics suggest that our river should support healthy populations: clear, cold water feeds our river most of the year and local regulations protect the fish. However, there is one thing we haven’t taken a very good look at: food availability. Conversations with local biologists and anglers indicated that local macroinvertebrate populations may be limited in our river and differ dramatically from other local rivers. There may not be enough food in our river to support trout populations! While this study didn’t answer that question directly (yet), it does provide some insight into water quality in our rivers and streams.
Macroinvertebrates, such as these two giant salmonfly larvae, are indicators of water quality and provide food for fish. Photo courtesy of Marc Fryt.
Macroinvertebrates are powerful indicators of water quality and habitat. These aquatic bugs live in our local streams and rivers year round, making them susceptible to seasonal or intermittent pollution that may missed by water quality testing. Read on to find out what we found!
We were able to identify 20 different macroinvertebrate species in the Spokane River. The most common organism volunteers found was aquatic earthworms; we found 41 of them. The percent EPT, which means the percentage of bugs that are part of the orders Ephemeroptera, Plecoptera, and Trichoptera (May, Caddis, and Stoneflies), was just around 46%, which suggests a slightly polluted ecosystem. 50% and above would be an indicator of good water quality.
We also had a surprise! We found two flathead mayflies! Dr. McNeely had mentioned that the presence of flathead mayflies, which are not tolerant of heavy metal pollution, was a good sign, as she had not seen them before in our river. We also found lots of salmonfly larvae, the largest species of stonefly in the world! Very cool!
Pollution from Hangman Creek is visible throughout the winter and spring runoff seasons.
On August 13th we sampled Hangman Creek. Hangman Creek has long been known as the most polluted stream in Washington State, at least when looking at non point source pollution, like temperature, dissolved oxygen, nutrients, and more.
The most abundant invertebrates people we found were water boatmen. The percent EPT, which means the percentage of bugs that are part of the orders Ephemeroptera, Plecoptera, and Trichoptera (may, stone, and caddisflies), was around 28.1 percent, which is indicative of poor water quality. 50% and above EPT is typically associated with good water quality. Of course, in Hangman Creek, a muddy and warm environment we found tolerant bugs too. We found leeches and snails, both of which are tolerant of poor water quality.
Sampling macroinvertebrates is a great way to get outside and in the creek!
The most abundant invertebrates people we found were water boatmen. The percent EPT, which means the percentage of bugs that are part of the orders Ephemeroptera, Plecoptera, and Trichoptera (may, stone, and caddisflies), was around 28.1 percent, which is indicative of poor water quality. 50% and above EPT is typically associated with good water quality. Of course, in Hangman Creek, a muddy and warm environment we found tolerant bugs too. We found leeches and snails, both of which are tolerant of poor water quality.
Some of the species that were found are actually indicators of decent water quality even though some of these metrics tell us otherwise. Mayfly presence suggests that sensitive organisms can survive in the creek, albiet not in the proportions that show good water quality. List to Dr. McNeely describe the organisms we found below. This aligns with water quality monitoring in Hangman Creek that shows small improvements in metrics like water clarity (turbidity), thanks to riparian restoration work in the watershed. However, water quality must improve much further to support designated uses like salmon restoration and redband trout spawning, rearing and migration.
Both the Spokane River and Hangman Creek’s macroinvertebrates reflect what we know about our local water quality. The Spokane River, while cold and clear, has pollution issues such as heavy metals. Hangman Creek’s bugs show that the creek has a long way to go in it’s recovery. To determine if our local trout populations are limited by food availability, we’ll need a more detailed study.