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What is the current situation?
Zion National Park Service (NPS) and the Utah Division of Water Quality (DWQ) have been monitoring benthic cyanobacteria in the North Fork of the Virgin River since July 7, 2020. Benthic cyanobacteria mats have been observed in varying densities within the river from The Narrows in Zion National Park down to Confluence Park in LaVerkin, Utah.
Routine monitoring and sampling continues both inside and outside the Park in order to gain a better understanding of the ongoing recreational risk from benthic cyanobacteria.
Cyanotoxin analysis has shown that anatoxin-a exists in high concentrations in the cyanobacteria mats and within the water column when mats are disturbed.
What are benthic cyanobacteria?
Cyanobacteria are a natural part of aquatic environments. While some harmful algal blooms (cyanobacteria blooms) are suspended in the water column and can be seen as bright green scum, others (benthic) attach themselves to the bottom of rivers and lakes. Benthic cyanobacteria 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, unlike cyanobacteria growing in the water column. Sometimes these mats detach and float to the surface, where wind and current can transport them to other locations or wash them up on the shore.
Similar to cyanobacteria we see in lakes, not all benthic cyanobacteria produce toxins but some species do. If toxins are present in sufficient concentrations, ingestion or contact can cause serious illness to humans and death to animals.
The likely cyanobacteria blooming in the Virgin River is the genus Tychonema. It forms colonies that can be red, yellow, tan, green, brown, or black in color. It produces the cyanotoxin called anatoxin-a, which impacts the nervous system.
What is the risk to recreators in the Virgin River?
Some cyanobacteria may produce dangerous liver and nervous system toxins; when in abundance, toxin concentrations can reach levels that affect the health of people, pets, and livestock. CHILDREN ARE ESPECIALLY VULNERABLE TO CYANOTOXINS. Anatoxin-a can be absorbed through eyes, nose, or mouth by swimming in or submerging accidentally or unknowingly into contaminated water. Symptoms include skin rash, salivation, drowsiness, tingling, burning, numbness, pain, incoherent speech, muscle contractions or twitching, vomiting, and diarrhea.
Humans and animals can ingest varying amounts of the benthic growth material and/or toxins, making exposure risk difficult to characterize compared to a water column or surface bloom. Even very small pieces of the cyanobacterial growth may contain enough cyanotoxin to cause harm and these pieces may be invisible.
The NPS, DWQ, and Utah Department of Health (DOH) have worked in the past weeks to characterize exposure risk of benthic cyanobacteria found in the Virgin River in order to better compare toxin results to the current DWQ/DOH HAB Guidance and recreational thresholds. These thresholds are set at 15 μg/L 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 are currently much greater than the DWQ/DOH recommended danger advisory threshold for cyanotoxins dissolved in water. More specifically:
- Very high anatoxin-a levels have been found within the benthic cyanobacteria mats themselves. Lab analyses are ongoing, but toxins within the mats in all samples are greater than 550μg/L of anatoxin-a.
- All water column samples taken without disturbing the cyanobacterial mats have been free of anatoxin-a.
- On July 21, 2020, 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.
What action is taken inside Zion National Park?
In response to new sample results provided on July 15 from the EPA, Zion National Park has issued a DANGER advisory for the parts of the North Fork of the Virgin River within the park. The advisory states the public should “AVOID CONTACT WITH THESE WATERS UNTIL FURTHER NOTICE: HARMFUL ALGAE PRESENT”
Dogs must be kept on a leash. If a pet breaks away and gets 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.
What action is taken outside of the Park?
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.
- Keep animals away.
- Do not ingest the water.
- Clean fish well and discard guts.
Pet owners should be careful not to let animals play in the river, drink from the river, or eat algal scum.
This warning does not apply to Quail Creek Reservoir, Sand Hollow Reservoir, or the Santa Clara River basin.
Is drinking water safe?
The Utah Division of Drinking Water is working with local utilities to ensure finished 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. Advanced water treatment technologies can remove cyanotoxins. The Town of Springdale will continue testing finished drinking water to make sure the water is safe.
How do benthic cyanobacteria affect agricultural water use?
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.
Update July 10, 2020
The Southwest Utah Public Health Department has issued a Warning Advisory for portions of the North Fork of the Virgin River after toxin test results for anatoxin-a exceeded the recreational health-based threshold for a Warning Advisory. Samples were collected after a dog died on July 4, 2020, shortly after playing in the river. Harmful cyanobacteria were subsequently found in multiple areas of the Virgin River where the incident occurred. Zion National Park has posted signs warning visitors not to swim or submerge themselves in the river and to keep pets out of the water.
The Warning Advisory does not apply to Quail Creek Reservoir, Sand Hollow Reservoir, or the Santa Clara River basin.
The Division of Water Quality (DWQ), Zion National Park, and local authorities will collect follow-up samples next week.
Anatoxin-a is a potent neurotoxin that can cause seizures, tingling, numbness, and other neurological symptoms. Toxin test results received July 10, 2020, show anatoxin-a concentrations greater than 55 micrograms per liter (µg/L) in some samples. The health-based recreational threshold for a Warning Advisory is 15 µg/L of anatoxin-a.
The Utah Department of Environmental Quality’s Division of Drinking Water (DDW) is working with local utilities to ensure finished (treated) drinking water that uses Virgin River water as its source is free of cyanotoxins. The Washington County Water Conservancy District, Zion National Park, and the Towns of Virgin and Rockville are not currently using the Virgin River as a drinking water source.
Advanced water treatment technologies can remove cyanotoxins. To date, tests of Springdale drinking water and agricultural water have not detected the presence of cyanotoxins. The Town of Springdale will continue testing finished drinking water to ensure it is safe.
Customers that use culinary water to supplement secondary water should make sure there is not a substantial demand on the system. Residents can avoid potential cross-connection contamination risks by not leaving a culinary water hose in a secondary water basin (such as an animal watering trough) as it can potentially pull secondary water into the culinary system and contaminate drinking water.
The Utah Department of Agriculture and Food (UDAF) suggests that livestock producers provide a different drinking-water source for livestock and restrict their access to the Virgin River wherever possible. Note: there is limited information on plant uptake of toxins. Farmers, irrigators and residents can protect themselves from toxin exposure by practicing good hygiene, especially in areas that come in contact with irrigation water.
A Warning Advisory indicates a moderate relative probability of acute health risk, toxigenic cyanobacteria cell densities between 100,000 and 10,000,000 cells per milliliter (cells/mL), microcystin levels between 8 and 2,000 micrograms per liter (µg/L), cylindrospermopsin levels greater than 15µg/L, or anatoxin-a levels from 15 µg/L to 90 µg/L.