North Fork of the Virgin River Algal Bloom Monitoring 2020

• Cyanobacteria may produce dangerous liver and nervous system toxins; toxin concentrations can reach levels that affect the health of people, pets, and livestock.
• Children are especially vulnerable to cyanotoxins.
• Toxins can be absorbed through eyes, nose, or mouth by swimming in contaminated water – very small or even invisible pieces of the cyanobacterial growth may contain enough toxin to cause harm.
• Symptoms include skin rash, salivation, drowsiness, tingling, burning, numbness, pain, incoherent speech, muscle contractions or twitching, vomiting, and diarrhea.

Since July 2020, the National Park Service (NPS) in Zion National Park has been routinely collecting both cyanotoxin and toxigenic cell count densities from harmful algal blooms on a monthly basis in several water bodies inside park boundaries. During this time, NPS, the Division of Water Quality (DWQ), and the Utah Department of Health (UDOH) have developed interim data-driven decision guidance for waterbody advisories during harmful algal blooms in Zion National Park.

Following this new guidance criteria, for the month of November, although cyanotoxins were still present, concentrations were below the Danger Advisory thresholds in the North Fork Virgin River, Taylor Creek, and North Creek waterbodies and were below Warning Advisory thresholds in LaVerkin Creek.

With lower cyanotoxin concentrations, The North Fork Virgin River, Taylor Creek, and North Creek Danger Advisories will be downgraded to a Warning Advisory and LaVerkin Creek will be downgraded to a Health Watch.

• During a Warning Advisory and Health Watch, do not submerge your head in the water. Toxins can enter the body by swallowing water or through the nose, eyes, or open wounds.
• Do not drink river water. Toxins cannot be filtered out by standard hiking filtration methods.
• Dogs must be kept on a leash. If pets get into the river, remove them from the water immediately, rinse off their fur thoroughly, and monitor for symptoms of toxin poisoning. A dog can die in as little as 15 minutes from anatoxin-a poisoning.
• Permitted waterbody activities, such as permitted canyoneering, are allowed.

In other areas of the North Fork of the Virgin River, outside of Zion National Park borders, the Southwest Utah Public Health Department has issued a public health warning. Signs have been posted by individual cities and towns to advise recreators of the risks associated with exposure. Residents should adhere to these guidelines:

• Do not swim in the signed area
• Avoid areas of algae scum
• Do not let animals play in the river, drink from the river, or eat algal scum
• Do not ingest the water
• Clean fish well and discard guts

This warning does not apply to Quail Creek Reservoir, Sand Hollow Reservoir, or the Santa Clara River basin.

The Utah Division of Drinking Water is working with local utilities to ensure drinking water that originates from the river is free of cyanotoxins. Currently, the Washington County Water Conservancy District, Zion National Park, and the Towns of Virgin and Rockville are not using the North Fork of the Virgin River as a drinking water source. Continued daily tests of Springdale drinking water and agricultural water have not detected the presence of cyanotoxins. The Town of Springdale will continue testing drinking water to make sure the water is safe.

The Utah Department of Agriculture and Food suggests that livestock producers provide a different drinking water source for livestock and restrict livestock access to the North Fork of Virgin River where possible. There is limited information on plant uptake of cyanotoxins. The main concern is protecting irrigators from these cyanotoxins. Practice good hygiene, especially those areas that come in contact with irrigation water.

The NPS, DWQ, and UDOH have worked to characterize exposure risk of benthic cyanobacteria in the Virgin River in order to better compare toxin results to the current DWQ/DOH HAB Guidance and recreational thresholds.

Benthic cyanobacteria attach themselves to the bottom of rivers and lakes and can appear as mats on rocks, submerged debris, sand, cobbles, or plants attached to the bottom of a waterbody.The water can appear clear where these mats are growing. Recreational thresholds are set at 15 μg/L (micrograms per liter) of anatoxin-a for a Warning Advisory and 90 μg/L of anatoxin-a for a Danger Advisory.

Cyanotoxin levels detected in the cyanobacterial growth and within the water column after the mats are disturbed have been much greater than the DWQ/DOH recommended danger advisory threshold for cyanotoxins dissolved in water. More specifically:

• In the summer of 2020, very high anatoxin-a levels were found within the benthic cyanobacteria mats themselves. Toxins within the mats, in all samples, were greater than 550μg/L of anatoxin-a.
• All water column samples taken without disturbing the cyanobacterial mats have been free of anatoxin-a.
• In July, a sampling design called ‘integrated disturbance’ began within the park. This involves collecting water column samples after a water quality scientist walked along a benthic cyanobacteria mat, imitating typical recreation in the river. All of the integrated disturbance water column sample results came back with anatoxin-a concentrations greater than 550 μg/L.