Mill Meadow Reservoir Algal Bloom Monitoring 2019

Update November 7, 2019

The Central Utah Public Health Department (CUPHD) has removed the Warning Advisory on Mill Meadow Reservoir. Toxin test results received from the Utah Public Health Lab (UPHL) for samples collected by the Division of Water Quality (DWQ) at the North Shore on October 24, 2019, showed microcystin levels well below the recreation health-based threshold for a Warning Advisory. Anatoxin-a levels, however, exceeded the recreation health-based threshold for a Warning Advisory.

The close of the monitoring season and removal of advisories doesn’t mean HABs are no longer present, but rather that monitoring data won’t be collected during the colder months to verify their presence. HABs can persist throughout the fall and winter and can pose a potential threat to humans and pets. It’s important for recreators to recognize the signs of a bloom and take appropriate precautions.

Recreators are advised to stay out of the water and avoid any contact with water or scum if they suspect a harmful algal bloom. Hunters and fishers should clean waterfowl and fish well and discard all guts.

Data Summary

North Shore

• Sample date: October 24, 2019
• Sample type: Elbow-depth integrated composite sample
• Microcystin: <2.0 micrograms per liter (µg/L)
• Anatoxin-a: 0.14 µg/L

Update October 29, 2019

Toxin test results received from the Utah Public Health Lab (UPHL) for samples collected by the Division of Water Quality (DWQ) at the south end of Mill Meadow Reservoir on October 10, 2019, showed anatoxin-a levels exceeded recreation health-based threshold for a Warning Advisory. Microcystin levels were below the advisory threshold. Cyanobacteria cell-count concentration results are pending from PhycoTech.

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.

Mill Meadow Reservoir remains under a Warning Advisory.

Data Summary

• Sample date: October 10, 2019
• Sample type: Elbow-depth integrated composite sample
• Microcystin: 0.217 micrograms per liter (µg/L)
• Anatoxin-a: 0.13 µg/L

Update September 16, 2019

The Central Utah Public Health Department (CUPHD) issued a Warning Advisory for Mill Meadow Reservoir on September 16, 2019.

Cyanobacteria cell count concentrations for samples collected by the Division of Water Quality (DWQ) at the north end of Mill Meadow Reservoir on September 11, 2019, exceeded the recreation health-based threshold for a Warning Advisory. Aphanizomenon was the primary taxon in the samples. Toxin test results received from the Utah Public Health Lab (UPHL) showed microcystin levels also exceeded the recreation health-based threshold for a Warning Advisory. Anatoxin-a levels were below the advisory threshold.

The DWQ monitoring crew observed visible cyanobacteria that resembled grass clippings, isolated clumps of bloom material, and cyanobacteria that resembled spherical nodules. These cyanobacteria were consistent throughout the water column. The crew observed a lot of past bloom material along the shore.

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.

Data Summary

• Sample type: Elbow-depth integrated composite sample
• Sample date: September 11, 2019
• Microcystin: 4.2 micrograms per liter (µg/L)
• Anatoxin-a: <0.10 µg/L
• Cyanobacteria cell counts: 90,021 cells per milliliter (cells/mL)

Update August 30, 2019

The Division of Water Quality (DWQ) received a report of a cyanobacteria bloom at Mill Meadow Reservoir on August 27, 2019. It’s recommended that the public not swim or water ski in areas of scum, avoid boating in areas of scum, not ingest untreated water, and keep animals away from the water. Visitors are cautioned to be mindful of water conditions, as blooms may move or disperse depending on temperature, wind, and weather.

The Central Utah Health Department will collect samples at Mill Meadow Reservoir next week.