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Deer Creek Reservoir Algal Bloom 2017

Update November 15, 2017

The Wasatch County Health Department saw a decrease in cyanobacteria levels at Deer Creek Reservoir over the last few weeks. The health department collected samples at Island Resort and Charleston Day Use Area on November 14, 2017. The sampler reported no visual evidence of current cyanobacteria blooms aside from some dried residue along the shoreline. Toxin strip test results on the sample was non-detect for microcystin and anatoxin-a.

Given the lack of visual evidence of continued algal blooms, the test strip results, and the significant decline in potential human exposure due to a decrease in visitors to the area, Wasatch County Health has decided to remove all warning signs and lift the warning advisory.


Update October 26, 2017

The Utah Public Health Lab ran ELISA tests on samples collected by the Wasatch County Health Department on October 17, 2017, at two locations at Deer Creek Reservoir. Microcystin levels were exceedingly high, ranging from 59 micrograms per liter (µg/L) at Rainbow Bay to825 µg/L at the Island Park Marina.

Warning signs remain posted at areas affected by high cyanobacteria/toxins on the reservoir.

Warning Advisory for Deer Creek Reservoir

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

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

Update October 19, 2017

The Wasatch County Health Department (WCHD) posted warning signs at Rainbow Bay after toxin strip-test results from a sample collected on October 17, 2017, showed microcystin levels greater than 10 micrograms per liter (µ/L) in the Bay.

WCHD also posted warning signs at the Charleston Day Use Area and along the northwest corner of the reservoir after staff identified blooms in these areas. The health department will continue to monitor the reservoir for the presence of cyanobacteria at other public-access areas.


Update October 18, 2017

During an E. coli monitoring expedition at recreational areas on October 17, 2017, Division of Water Quality (DWQ) field staff collected cyanobacteria samples at Island Marina and Rainbow Bay on Deer Creek Reservoir. Toxin strip tests for both locations were >10 micrograms per liter (µg/L) for microcystin, which is above the UDEQ-UDOH recommended health-advisory thresholds for a warning advisory for recreational waters. Strip test results were non-detect for anatoxin-a and cylindrospermopsin. The presence of microcystin outside the Island Marina area indicates that cyanobacteria cells are accumulating in other areas of the reservoir.

Samples were sent to the Utah Public Health Lab and Utah Department of Agriculture and Food for ELISA testing to quantify the strip-test results. Lab results should be available within the next three business days.

Warning Advisory for Deer Creek Reservoir

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. Advisory actions:

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

Update October 13, 2017

Wasatch County Health took a sample at the Island Park Marina on October 6, 2017. The toxin strip test results were >10 micrograms per liter (µ/L) for microcystin. According to UDOH-UDEQ health guidance, microcystin levels >4 µg/L trigger a recreational warning advisory. The current Warning Advisory remains in place for this area of the reservoir.

Warning Advisory for Deer Creek Reservoir

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

  • Do not swim or water ski
  • Do not drink the water
  • Keep pets and livestock away
  • Clean fish well and discard guts
  • Avoid areas of scum when boating
Red dots show the warning signs locations

Cove area sampling point


Update September 15, 2017

Deer Creek Reservoir Continuous BGA (blue-green algae) results from September 9, 2017 to September 15, 2017

Continuous BGA (blue-green algae) results from 9/9 to 9/15


Update September 14, 2017

Toxin tests strips on samples were non-detect for microcystin, cylindrospermopsin, and anatoxin-a. Wasatch County Health Department will sample again on September 18, 2017.

Warning Advisory for Deer Creek Reservoir

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

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

Update September 13, 2017

Samples were taken along both the shore and by the dock. Toxin strip tests were conducted on these samples. Shore results > 10 micrograms per liter (µg/L) for microcystin, and dock results were 0 µg/L for microcystin. The Wasatch County Health Department posted warnings signs at Island Park and will continue to monitor the site and remove signs when appropriate.

Warning Advisory for Deer Creek Reservoir

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

  • Do not swim or water ski
  • Do not drink the water
  • Keep pets and livestock away
  • Clean fish well and discard guts
  • Avoid areas of scum when boating
Red dots show the warning signs locations

Red dots show the warning signs locations.

Deer Creek Algal Bloom



Update September 12, 2017

Lab testing from September 11, 2017, samples resulted in microcystins of >100 micrograms per liter (µg/L). According to UDOH-UDEQ health guidance, microcystin levels >4 µg/L trigger a recreational warning advisory.

The Central Utah Water Conservancy District (CUWCD) collected phytoplankton samples at several locations in the reservoir. The Division of Water Quality (DWQ) is waiting for the lab results showing the cyanobacteria cell-count densities from these phytoplankton samples. CUWCD reported that the algal mat has almost dispersed.

Warning Advisory for Deer Creek Reservoir

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

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

Deer Creek Algal Bloom


September 11, 2017

Division of Water Quality (DWQ) monitoring crews encountered a shoreline-localized cyanobacteria bloom on Deer Creek reservoir during routine E. coli monitoring on Monday September 11. The bloom was observed along the shoreline at Island Park Marina, but did not appear to be located in the open water, Rainbow Bay, or the main boat launch.

The monitoring crew collected two samples: a surface sample and a depth-integrated sample. Toxin strip tests on the surface sample tested >10 micrograms per liter (µg/L) for microcystins; the integrated sample had a result of 2.5 µg/L. According to UDOH-UDEQ health guidance, microcystin levels >4 µg/L trigger a recreational warning advisory. Concentrations for cylindrospermopsin and anatoxin-a were non-detect.

DWQ sent the samples to the Utah Public Health Lab on September 12, 2017, for Enzyme-Linked Immunosorbent Assay (ELISA) for further microcystins testing.

Warning Advisory for Deer Creek Reservoir

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

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

Deer Creek Algal Bloom

Algal Bloom observed along shoreline in Island Park Area