Mill Meadow Reservoir Algal Bloom Monitoring 2018

Warning Advisory

  • Do not swim or water ski
  • 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.


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Mill Meadow Reservoir sits at approximately 7,600 foot elevation and is located northwest of Loa in the Fish Lake Mountains. Water from the reservoir is primarily used for irrigation and agricultural purposes, but the waterbody is also a popular camping, boating and fishing destination.

Update September 20, 2018

Mill Meadow Northwest end, September 20, 2018

The Division of Water Quality (DWQ) visited Mill Meadow Reservoir on September 13, 2018. The monitoring crew observed cyanobacteria that looked like grass clippings suspended in the water column throughout the reservoir. The northwestern part of the reservoir had the thickest accumulation of cyanobacteria. This accumulation formed a scum on the surface of the water.

Toxin-test results received by DWQ from the Utah Public Health Lab (UPHL) showed anatoxin-a and microcystin levels exceeding the recreation health-based threshold for a Warning Advisory. Microcystin levels were particularly high at 190 micrograms per liter (µg/L), almost 48 times the threshold for a Warning Advisory.

Due to elevated toxin levels in Mill Meadow Reservoir, the Utah Department of Agriculture and Food (UDAF) recommends that farmers and ranchers prevent livestock from drinking from the reservoir. UDAF advises producers to find alternative water sources until conditions improve.

Toxin Test Results

  • Surface sample collected at the northwestern end of the reservoir.
  • Anatoxin-a: 0.10 µg/L
  • Microcystin: 190 µg/L

The Warning Advisory for Mill Meadow Reservoir remains in place.


Update September 4, 2018

Toxin test results and cyanobacteria cell-count concentrations for a surface sample collected at the north end of the reservoir by the Division of Water Quality (DWQ) on August 22, 2018, show microcystin levels and cyanobacteria cell counts exceeding the recreation health-based threshold for a Danger Advisory.

The Highline Canal associated with this waterbody was also tested for toxins by the Utah Department of Agriculture and Food (UDAF) lab. Anatoxin-a levels were <0.1 µg/L and microcystins levels were 0.39 µg/L, so it does not appear that toxins have entered the canal at this time. However, should winds shift and move the bloom towards the canal, conditions there could change dramatically.

The Utah Public Health Lab (UPHL) found microcystin levels >2500 micrograms per liter (µg/L) after 500x dilution. The lab will continue to dilute the sample for final quantification of microcystin levels. These levels well exceed the >2000 µg/L threshold for a Danger Advisory. Anatoxin-a levels exceed the recreation health-based threshold for a Warning Advisory. Toxigenic cyanobacteria cell-count densities were 21,900,398 cells per milliliter (cells/ml), over twice the recreation health-based threshold for a Danger Advisory.

Due to elevated toxin levels in Mill Meadow Reservoir, the Utah Department of Agriculture and Food (UDAF) recommends that farmers and ranchers prevent livestock from drinking from the reservoir. UDAF advises producers to find alternative water sources until conditions improve.

The Warning Advisory remains in place for Mill Meadow Reservoir.


Update August 21, 2018

Due to elevated toxin levels in Mill Meadow Reservoir, the Utah Department of Agriculture and Food (UDAF) recommends that farmers and ranchers prevent livestock from drinking from the reservoir. UDAF advises producers to find alternative water sources until conditions improve. (See August 18 update for more info)

Cyanobacteria cell-count concentrations from a sample collected August 8, 2018, in Mill Mountain Reservoir showed high cell counts of 6,482,538 cells per milliliter (cells/ml). These cell densities exceed the recreation health-based threshold for a Warning Advisory. The reservoir remains under a Warning Advisory based on microcystin levels and cyanobacteria cell-count concentrations.

Warning Advisory for Mill Meadow 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 ingest the water
  • Keep pets and livestock away
  • Clean fish well and discard guts
  • Avoid areas of scum when boating

Update August 18, 2018

Due to elevated toxin levels in Mill Meadow Reservoir, the Utah Department of Agriculture and Food (UDAF) recommends that farmers and ranchers prevent livestock from drinking from the reservoir. UDAF advises producers to find alternative water sources until conditions improve.

“The best guidelines I have suggest that beef cattle consuming a primary water source with microcystin levels over 200 µg/L (micrograms per liter) could start to experience serious health effects in as little as 24 hours,” said Dr. Chelsea Crawford, Assistant State Veterinarian, UDAF.

Latest lab results show microcystin levels of 339 µg/L in the reservoir.


Update August 17, 2018

Utah Public Health Lab (UPHL) toxin test results show high microcystin levels in the reservoir. The lab confirmed microcystin levels of 339 micrograms per liter (µg/L) after 100 times dilution. This result is well above the 50 µg/L reported yesterday pending further dilutions. The reservoir remains under a Warning Advisory.

Warning Advisory for Mill Meadow 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 ingest the water
  • Keep pets and livestock away
  • Clean fish well and discard guts
  • Avoid areas of scum when boating

Update August 16, 2018

The Central Utah Health Department has issued a Warning Advisory for Mill Meadow Reservoir due to microcystin and anatoxin-a levels that exceed the recreation health-based threshold. Lab results show microcystin levels in excess of 50 micrograms per liter (µg/L). These levels could go even higher with further dilutions by the lab. Anatoxin-a levels were relatively low (0.5 µg/L) but the presence of the toxin triggers a Warning Advisory.

Health department officials are posting signs today to alert visitors of the advisory.

Warning Advisory for Mill Meadow 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 ingest the water
  • Keep pets and livestock away
  • Clean fish well and discard guts
  • Avoid areas of scum when boating

Update August 15, 2018

Lab results from the Utah Public Health Lab (UPHL) for the sample collected at Mill Meadow Reservoir on August 8, 2018, showed microcystin levels >5 micrograms per liter (µg/L). Toxin levels will likely exceed 50 µg/L with further dilutions by the lab. Test results also showed 0.5 µg/L of anatoxin-a in the sample. Toxin levels for both anatoxin-a and microcystins exceed the recreation health-based threshold for a Warning Advisory.


Update August 14, 2018

Mill Meadow Reservoir August 8, 2018

Mill Meadow Reservoir August 8, 2018

The Division of Water Quality (DWQ) visited Mill Meadow Reservoir on August 8, 2018, and observed a cyanobacteria bloom across the entire reservoir. The northern end of the reservoir contained a greater accumulation/concentration of cells. Visible cyanobacteria in the reservoir resembled grass clippings. The monitoring crew collected a surface sample.

Toxin strip tests exceeded the recreation health-based threshold for a Warning Advisory for both anatoxin-a and microcystin.

Toxin Test Strip Results

  • Anatoxin-a: <0.4 micrograms per liter (µg/L)
  • Microcystin: >10 µg/L

The sample was sent to the Utah Public Health Lab (UPHL) and Utah Department of Agriculture and Food (UDAF) lab for confirmation of toxin levels.