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Mantua Reservoir Algal Bloom 2017

| Updates | Data |

Mantua Reservoir in located in a sardine canyon near Mantua, Utah. It sits at an elevation of 5,000 feet and is a popular recreation area for fishing, boating, and water recreation.

Update November 6, 2017

Brigham City collected a sample from the Mantua Boat Dock on October 31, 2017. Toxigenic cyanobacteria cell-count concentrations continue to exceed the 20,000 cells/ml threshold for a warning advisory under UDOH-UDEQ health-based guidance. Pseudanabaena showed a marked increase, rising from >70,000 cells per milliliter (cells/ml) to >180,000 cells/ml. This taxon is capable of producing microcsytin and anatoxin-a. Aphanocapsa and Synechocystis were also present in the sample, but in much lower concentrations.

The Utah Public Health Lab toxin testing showed 0.265 micrograms per liter (µg/L) of microcystin, well below the recreational health-based threshold of 4 µg/L. Anatoxin-a results are pending from the Utah Department of Agriculture and Food (UDAF) lab, but DWQ scientists don’t anticipate detectable concentrations from these particular cyanobacteria taxa.

Warning Advisory for Mantua 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 6, 2017

A sample collected by Brigham City on September 28, 2017, showed cyanobacteria cell-count concentrations of 88,444 cells per milliliter (cells/ml). These results exceed the 20,000 cells/ml threshold for a warning advisory under UDOH-UDEQ health-based guidance.

Multiple cyanobacteria taxa capable of producing toxins are present in the reservoir, primarily Pseudanabaena (70,599 cells/ml) and Synechocystis (9,909 cells/ml). Both genera can produce microcystin. Pseudanabaena can produce anatoxin-a.

Toxin test-strip results were non-detect for microcystin.

Warning Advisory for Mantua 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 20, 2017

The recreational warning issued September 11, 2017 on Mantua Reservoir will remain in effect. Samples collected September 19, 2017 indicate that although microcystin levels have decreased to 1 µg/L, anatoxin-a was detected at 0.4 µg/L based on toxin test strip results. This result exceeds the anatoxin-a warning advisory threshold in UDEQ-UDOH health advisory guidance. Additionally, cyanobacteria cell counts from the sample collected on September 11, 2017 was greater than 46,000 cells/ml which exceeds the 20,000 cell/ml warning advisory further confirms the advisory.

Warning Advisory for Mantua 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 12, 2017

The Bear River Health Department has issued a water recreational advisory for Mantua Reservoir based on toxin test strip results of >5 µg/L for microcystin for a sample collected September 7, 2017. This result exceeds the 4 µg/L warning advisory threshold in UDEQ-UDOH health advisory guidance. The health department is posting signs at the reservoir to alert the public of the presence of cyanobacteria and cyanotoxins in the reservoir.

Warning Advisory for Mantua 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 8, 2017

Toxin strip testing on a sample collected on Mantua Reservoir by Utah Water Watch on September 7, 2017, tested > 5 µg/L for microcystin. This result exceeds the 4 µg/L warning advisory threshold in UDEQ-UDOH health advisory guidance.The primary cyanobacteria present in the reservoir, Aphanizomenon, is known to produce microcystin. Toxin strip testing was non-detect for anatoxin-a.

Utah Water Watch will return to the reservoir on September 11, 2017, to collect an additional sample for toxin strip testing, cyanobacteria cell-count concentration, genera identification, and ELISA testing by the Utah Public Health Lab.


Update August 18, 2017

A harmful algal bloom was reported to be in progress on August 16, 2017, primarily on the east side of Mantua Reservoir. The cyanobacteria genus responsible for the bloom was tentatively identified as Aphanizomenon, and a sample was collected for analysis by Utah Water Watch. Toxin test strips were non-detect for anatoxin-a, microcystin, and cylindrospermopsin. No report of fish, wildlife, or livestock deaths.