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Matt Warner Reservoir

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Matt Warner Reservoir is one of three lakes in located in the Diamond Mountain area near Vernal, Utah. The reservoir, along with Calder and Crouse Reservoir, is a popular fishing spot in the northern Uintas.

Matt Warner experiences periodic harmful algal blooms, the most deadly one occurring in 2004, with a reoccurrence in 2010. Fifteen calves and three adult cows died from liver failure after drinking water from the reservoir during the 2004 toxic bloom. Sampling during this bloom showed the presence of Microcystis aeruginosa, a species of cyanobacteria that can produce microcystin, a powerful liver toxin.

The Division of Drinking Water (DWQ) is monitoring the continued presence of elevated concentrations of cyanobacteria in Calder and Matt Warner reservoirs and has set the “decrease in dominance of blue-green algae” as a target for its total maximum daily load (TMDL) restoration plans for these reservoirs.

Update August 9, 2017

DEQ’s District Engineer and the Tri-County Health Department inspected the reservoir on August 5, 2017, and observed numerous dead fish and crayfish on the shore and in the water. Blue-green stains along the shoreline indicated a cyanobacteria bloom. It appeared to both inspectors that the bloom peaked several days earlier and collapsed. The bloom appeared to be concentrated at the northern end of the lake due to winds.

The massive fish and crayfish kill does not appear to be caused by cyanotoxins but rather by low dissolved oxygen (DO) levels caused by bloom decomposition. Fish and other aquatic organisms need dissolved oxygen to breathe. When the biomass from algal blooms dies, its decomposition depletes the dissolved oxygen, leading to aquatic life mortality.

The Division of Wildlife Resources (DWR) took dissolved oxygen (DO) and temperature readings at all three reservoirs on August 8, 2017, and found astoundingly low DO levels, suggesting the bloom was likely massive and died quickly. DWR personnel also observed a large algal bloom in Calder Reservoir, and suspended algae and other plant matter floating in the water column at Crouse Reservoir that was much thicker than the other two reservoirs. Preliminary counts indicated approximately 800 fish deaths, although DWR believes more fish died. Many of the remaining fish were observed to be struggling to breathe.

DEQ’s District Engineer took samples at Matt Warner Reservoir during his August 5, 2017, inspection. This week, DWQ will conduct toxin strip tests on the samples and send them to a lab for identification of the cyanobacteria genera present in the water.