Otter Creek Reservoir Algal Bloom Monitoring 2019

Warning Advisory

  • Do not swim or water ski in this area.
  • Avoid areas of algae scum when boating.
  • Keep animals away.
  • Do not ingest the water.
  • Clean fish well and discard guts.

Report a Bloom

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.

Get BloomWatch App

Help us track cyanobacteria blooms with your smartphone. Go to cyanos.org for more info.

Update September 10, 2019

Otter Creek Reservoir, September 10, 2019

Toxin test results received from the Utah Public Health Lab (UPHL) for samples collected by the Division of Water Quality (DWQ) at the upper end of Otter Creek Reservoir on September 10, 2019, showed anatoxin-a levels exceeding the recreation health-based threshold for a Warning Advisory. Microcystin levels and cyanobacteria cell-count concentration results are pending.

A Warning Advisory indicates a moderate relative probability of acute health risk, cell-count density of 20,000 – 10 million cells per milliliter (cells/ml), microcystin levels of 4-2,000 micrograms per liter (µg/L), or anatoxin-a levels above non-detect.

Otter Creek Reservoir remains under a Warning Advisory.

Data Summary

  • Sample date: September 10, 2019
  • Sample type: Elbow-depth integrated composite sample
  • Anatoxin-a: 0.14 µg/L

Update August 23, 2019

Cyanobacteria cell-count results received by the Division of Water Quality (DWQ) on September 5, 2019, for samples collected at the upper end of Otter Creek Reservoir on August 22, 2019, were well the recreation health-based threshold for a Warning Advisory. Cyanobacteria cell-count concentrations dropped dramatically, from over 5.2 million cells per milliliter (cells/mL) in an August 14, 2019, surface sample to 4,503 cells/mL a week later. The primary taxon in the samples was Aphanizomenon, but Dolichospermum, Gloeotrichia, Microcystis, and Planktothrix were present in smaller quantities.

Toxin test results for anatoxin-a and microcystin were both non-detect. DWQ is now running new dilution curves for its enzyme-linked immunosorbent assay (ELISA) analysis for cyanotoxins. These different dilution ratios (1:1000 and 1:20) have changed the detection limit for microcystin from <0.10 micrograms per liter (µg/L) to <2.0 µg/L. The 1:20 dilution will detect toxin levels between 2 and 100 µg/L, and the 1:1000 dilution will detect toxin levels between 100 and 5,000 µg/L. These new dilution ratios should result in faster lab results. If further precision is needed, the lab will run additional dilutions.

The DWQ monitoring crew observed cyanobacteria resembling small cylindrical nodules in the water column during their August 22, 2019, visit to the reservoir. No other types of cyanobacteria were visible.

A Warning Advisory indicates a moderate relative probability of acute health risk, cell-count density of 20,000 – 10 million cells per milliliter (cells/ml), microcystin levels of 4-2,000 micrograms per liter (µg/L), or anatoxin-a levels above non-detect. The advisory for Otter Creek can be lifted if the next sample falls below the recreation health-based threshold for a Warning Advisory.

Otter Creek Reservoir remains under a Warning Advisory.

Data Summary

Elbow-depth integrated composite sample

  • Sample date: August 22, 2019
  • Microcystin: < 2.0 micrograms per liter (µg/L)
  • Anatoxin-a: <0.10 µg/L
  • Cyanobacteria cell counts: 4,503 cells per milliliter (cells/mL)

Update August 23, 2019

Toxin test results received late yesterday by the Division of Water Quality (DWQ) for the surface sample collected on August 14, 2019, show microcystin levels of 1900 micrograms per liter (µg/L) after 4000x dilution. These values approach but do not exceed the >2000 µg/L recreation health-based threshold for a Danger Advisory.

The DWQ monitoring crew returned to Otter Creek Reservoir on August 22, 2019, to collect additional samples.

A Warning Advisory indicates a moderate relative probability of acute health risk, cell-count density of 20,000 – 10 million cells per milliliter (cells/ml), microcystin levels of 4-2,000 micrograms per liter (µg/L), or anatoxin-a levels above non-detect.

The Warning Advisory for Otter Creek Reservoir remains in place.

Updated Data Summary

  • Surface sample
  • Sample Date: August 14, 2019
  • Microcystin: 1900 micrograms per liter (µg/L)
  • Anatoxin-a: 0.12 µg/L
  • Cell counts: 5,227,550 cells per milliliter (cells/mL)

Update August 21, 2019

Otter Creek Reservoir

Otter Creek Reservoir, August 14, 2019

Toxin test results received late yesterday by the Division of Water Quality (DWQ) for the August 14, 2019, surface samples at Otter Creek Reservoir showed anatoxin-a and microcystin levels exceeding the recreation health-based threshold for a Warning Advisory. Microcystin levels without dilution exceeded the recreation health-based threshold for a Danger Advisory, but these results are still preliminary. Further dilutions by the Utah Public Health Lab (UPHL) will be necessary to quantify microcystin concentrations.

Cyanobacteria cell-count concentrations were also at the upper range for a Warning Advisory at over 5.2 million cells per milliliter (cells/mL). The dominant taxon was Microcystis, a type of cyanobacteria that can produce liver and nerve toxins.

The DWQ monitoring crew will return to Otter Creek Reservoir today to collect additional samples.

A Warning Advisory indicates a moderate relative probability of acute health risk, cell-count density of 20,000 – 10 million cells per milliliter (cells/ml), microcystin levels of 4-2,000 micrograms per liter (µg/L), or anatoxin-a levels above non-detect.

The Warning Advisory for Otter Creek Reservoir remains in place.

Data Summary

Surface sample

  • Sample Date: August 14, 2019
  • Microcystin: >2,000 micrograms per liter (µg/L)
  • Anatoxin-a: 0.12 µg/L
  • Cell counts: 5,227,550 cells per milliliter (cells/mL)

Elbow-depth integrated composite sample

  • Sample Date: August 14, 2019
  • Microcystin: 14 micrograms per liter (µg/L)
  • Anatoxin-a: <0.10 µg/L
  • Cell counts: 75,234 cells per milliliter (cells/mL)

Update August 21, 2019

The Central Utah Public Health Department (CUPHD) issued a Warning Advisory for Otter Creek after samples collected by the Division of Water Quality (DWQ) on August 14, 2019, at the midway shore showed microcystin levels between 5 and 120 micrograms per liter (µg/L). These toxin levels exceed the recreation health-based threshold for a Warning Advisory. Health officials will be posting signs at the reservoir.

Toxin test results for surface samples are pending from the Utah Public Health Lab (UPHL). Further dilutions by UPHL will be necessary to quantify microcystin concentrations in the water-column sample that triggered the Warning Advisory. Cyanobacteria cell-count concentrations are also pending. DEQ will post updates as these results come in.

The DWQ monitoring crew observed three types of cyanobacteria on the reservoir. The dominant cyanobacteria were greenish-brown, spherical nodules that had accumulated on the shore and collected into mats in the water. The crew also saw cyanobacteria that resembled grass clippings and isolated clumps in the water column.

Otter Creek Reservoir, August 14, 2019

A Warning Advisory indicates a moderate relative probability of acute health risk, cell-count density of 20,000 – 10 million cells per milliliter (cells/ml), microcystin levels of 4-2,000 micrograms per liter (µg/L), or anatoxin-a levels above non-detect.

Elbow-depth Integrated Composite Sample

  • Sample Date: August 14, 2019
  • Microcystin: between 5 and 120 micrograms per liter (µg/L)
  • Anatoxin-a: <0.10 µg/L