Calder Reservoir Algal Bloom Monitoring 2019

Warning Advisory

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

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 August 13, 2019

Calder Reservoir, August 6, 2019

Toxin test results from samples collected at Calder Reservoir on August 6, 2019, were detect for anatoxin-a. Detection of anatoxin-a exceeds the recreation health-based threshold for a Warning Advisory. Microcystin levels were well below the advisory threshold. Cyanobacteria cell-count results from PhycoTech 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.

Calder Reservoir remains under a Warning Advisory.

Data Summary

  • Sample Date: August 6, 2019
  • Sample type: Elbow-depth integrated composite sample
  • Microcystin: 0.264 micrograms per liter (µg/L)
  • Anatoxin-a: 0.124 µg/L

Update August 5, 2019

Calder Reservoir, July 30, 2019

Cyanobacteria cell-counts from samples collected on July 30, 2019, at Calder Reservoir were at the upper end of the recreation health-based threshold for a Warning Advisory. Toxin-test results for microcystin and anatoxin-a were both well below the health advisory threshold.

The Division of Water Quality (DWQ) monitoring crew observed visible cyanobacteria resembling small circular nodules and grass clippings. Cyanobacteria were evident on the surface and throughout the water column. The primary cyanobacteria taxon found in the samples was Aphanizomenon.

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.

Calder Reservoir remains under a Warning Advisory.

Surface sample

  • Sample Date: July 30, 2019
  • Microcystin: <0.10 micrograms per liter (µg/L)
  • Anatoxin-a: <0.10 µg/L
  • Cell Counts: 2,857,308 cells per milliliter (cells/mL)

Elbow-depth integrated composite sample

  • Sample Date: July 30, 2019
  • Microcystin: <0.10 micrograms per liter (µg/L)
  • Anatoxin-a: <0.10 µg/L
  • Cell Counts: 1,169,730 cells per milliliter (cells/mL)

Update July 22, 2019

Follow-up water samples collected by the Division of Water Quality (DWQ) on July 11, 2019, were below cyanobacteria cell-count and toxin recreation health-based thresholds.

Matt Warner Reservoir, a waterbody approximately five miles northwest, is connected to Calder Reservoir via Pot Creek and also under a harmful algal bloom advisory. Because water from Matt Warner can flow into Calder Reservoir, the Tri-County Health Department has chosen to maintain the Warning Advisory for Calder Reservoir.

While cell-counts remain below health-based advisory thresholds, the predominant species continues to be Aphanizomenon, a cyanobacteria taxon that can produce both microcystin and anatoxin-a.

  • Calder Reservoir Boat Ramp (elbow-depth integrated composite sample): <0.10 micrograms per liter (µg/L) of anatoxin-a; <0.10 µg/L of microcystin; cyanobacteria cell-count concentrations of 4,002 cells per milliliter (cells/mL)
Calder Reservoir, July 11, 2019

Calder Reservoir, July 11, 2019


Update July 11, 2019

Calder Reservoir Boat Ramp (elbow-depth integrated composite sample): <0.10 µg/L of anatoxin-a; <0.10 µg/L of microcystin; cyanobacteria cell-count concentrations of 4,002 cells/mL


Update July 3, 2019

Division of Water Quality (DWQ) scientists conducted follow-up sampling at Calder Reservoir on July 2, 2019. Cyanobacteria were still present but less abundant (visually) than the previous visit. Green clumps remained dispersed in the water column.

Scientists collected elbow-depth integrated composite samples at the boat ramp. Toxin test results from the Utah Public Health Lab (UPHL) on July 3, 2019, showed the samples were below the recreation health-based thresholds for an advisory.

  • Calder Reservoir Boat Ramp (elbow-depth integrated composite sample): <0.10 µg/L of anatoxin-a; <0.10 µg/L of microcystin

While the sample results were below advisory thresholds, the presence of a visible bloom can serve as cause for the issuance of an advisory, since toxin levels can vary from day to day.

Calder Reservoir remains under a Warning Advisory.


Update June 21, 2019

Calder Reservoir, June 11, 2019

The Division of Water Quality (DWQ) collected an elbow-depth integrated water sample at the Zelph Calder Reservoir Boat Ramp on June 11, 2019. The monitoring crew observed Isolated clumps of green cyanobacteria on the surface of the reservoir and throughout the water column.

DWQ received cyanobacterial cell-count concentration results from PhycoTech on June 20, 2019, of 103,720 cells per milliliter (cells/mL) at the boat ramp. These cell-count densities exceed the recreation health-based threshold for a Warning Advisory. Based on these data, the Tri-County Health Department has issued a Warning Advisory for the Zelph Calder Reservoir.

The Tri-County Health Department will be posting signs at the reservoir. Health officials will collect water samples next week.

Toxin screening tests were inconclusive and samples were delivered to the Utah Public Health Lab (UPHL) for further analysis. UPHL testing showed anatoxin-a and microcystin levels of <0.10 micrograms per liter (µg/L), which are well below the recreation health-based threshold for a Warning Advisory.

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.