Matt Warner Reservoir Algal Bloom 2017

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24-Hour DEQ Environment Incidents Line: (801) 536-4123

Call Utah Poison Control Center

If you believe you or your pet have been exposed to a harmful algal bloom, call (800) 222-1222.

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 Water Quality (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 30, 2017

The Utah Department of Agriculture and Food (UDAF) collected four samples in and around the reservoir on August 23, 2017. Samples were sent to the UDAF lab for Enzyme-Linked Immunosorbent Assay (ELISA) toxin testing. One sample from the north public access area tested at >5 micrograms per liter (µg/L) for microcystin, which exceeds the 4 µg/L warning advisory threshold in UDEQ-UDOH health advisory guidance. Samples at the West Boat Ramp and North Public Access Area detected a low level of anatoxin-a. While these results were at the low end of the warning-advisory threshold for anatoxin-a, any results above non-detect trigger a warning advisory under UDOH and UDEQ health-based guidance.

The Division of Water Quality (DWQ) sent the sample from the North Public Access Area to a lab for genera/species identification and cyanobacteria cell-count concentrations.

Sampling Date and Locations

August 23, 2017

  • East Boat Ramp
  • West Boat Ramp
  • North Public Access Area
  • West Bank of Cottonwood Dam by inflow from Bullock Reservoir


Enzyme-Linked Immunosorbent Assay (ELISA) toxin testing was conducted by the UDAF lab. LOQ stands for “less than the limit of quantitation;” this is the smallest amount that the laboratory considers to be reliably quantifiable. All samples tested LOQ for cylindrospermopsin.

  • East Boat Ramp: 0.364 µg/L of microcystin; LOQ for anatoxin
  • West Boat Ramp: 0.314 µg/L of microcystin; 0.067 µg/L of anatoxin-a
  • North Public Access Area: >5 µg/L of microcystin; 0.039 µg/L of anatoxin-a
  • West Bank of Cottonwood

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.