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Post-Treatment Monitoring

Benthic Invertebrates

Twenty-two benthic collection sites were developed by Joe Eilers of MaxDepth Aquatics in 2002. Site locations were based on historical sites from the Environmental Protection Agency and ODFW collections and were representative of the lake’s benthic population.

Sites included deep, shallow, weedy, non-weedy, hard bottom, and soft bottom sites. In 2004, ODFW added a site near Thielsen View Campground commonly referred to as the “shrimp beds” in the lake.

Sites were sampled in triplicate using a Petite Ponar dredge (Wildco #1728-G30) to sample an area of 152 mm x 152 mm per grab then hoisted to the boat using an electric crab pot puller. Each grab was put into a Wildco sieve bucket with #30 mesh to separate samples from substrate.

The entire sieved sample, pooled for each site was placed into a jar with denatured alcohol or sorted in the field. Each jar was then labeled with site number and date for later processing. Samples were identified by ODFW staff or professional taxonomists and split into groups. The benthic food index for the lake was calculated for samples by month.

Bottom-dwelling organisms, such as snails, insects, and shrimp-like creatures recovered rapidly and provided additional food for trout.

Species of invertebrates not seen in the previous decade have re-colonized the lake. These taxa include mayflies, caddisflies, snails, and bivalves/clams/mussels. Taxa that were rare during the last decade have become abundant, including amphipods (freshwater shrimp), leeches, and dragonflies.

ODFW has historically conducted benthic sampling in Diamond Lake to use as a tool to help manage and monitor the fishery. Benthic macro invertebrate data is a good indicator of water quality and lake health, availability of food for fish, and an important tool for aiding in determination of fish stocking rates.

The ODFW standard benthic sampling for Diamond Lake from 1948-present is done in October every year. As part of the Diamond Lake Restoration Project, intensity of sampling was increased to gather baseline data prior to treatment, and increased benthic sampling will continue post treatment to monitor recovery of the lake.

Benthic species identification was performed by ABR, Inc. See chart below for more information.

benthic biomass
Historical October Benthic Sampling

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