Algal bloom at Indian Creek |

Algal bloom at Indian Creek

Staff Reports

Alpine Watershed Group in coordination with the Lahontan Regional Water Quality Control Board has initiated a new harmful algal bloom monitoring program to more closely track the water quality in some of Alpine County’s most popular summer recreation reservoirs. The group began these monitoring efforts in late June and plans to continue through mid-October at Red Lake, Indian Creek, and Wet Meadow reservoirs at least once a month.

On July 22, Alpine Watershed Group conducted routine sampling at Indian Creek Reservoir. Test results measured levels of cyanotoxin microcystins at 4.39 micrograms per liter, which is above the 0.8 micrograms per liter caution action trigger level established for posting signs at recreational waters for the protection of human health. South Tahoe Public Utility District, who manages the property, posted caution signs at Indian Creek Reservoir to warn lake users to stay away from algae and scum in the water and avoid drinking, or having pets drink the water. Fishing is allowed, but anglers should clean fish fillets with tap water before cooking and throw away the fish guts.

Cyanobacteria, also known as blue-green algae, are naturally present in waterbodies and are an integral part of our ecosystems. When provided the right conditions cyanobacteria can develop into a bloom from excessive growth. Blooms, if stimulated enough, can decrease water quality but are only considered an immediate threat to human and animal health if emitting toxins.

Not all cyanobacteria produce harmful toxins, but in rare cases, toxin levels may be concentrated enough to cause rashes, diarrhea, or vomiting. If you see signs of a bloom, such as discolored, pea-green water, surface scum, floating algae, stay out of the water.

Warmer air and water temperatures, high nutrient levels, and slow and stagnant water can cause cyanobacteria to multiply at an excessive rate and turn in to a bloom. When present, the algal scum can be a variety of colors such as fluorescent blue, green white, red or brown. Blooms can have more than one color present and may look like thick paint floating on the water and give off a foul odor. Blooms may move to different locations of the lake by wind or wave.

The group will conduct monitoring at Indian Creek Reservoir again on Aug. 19. The district, which takes a minimum of three cyanobacteria water samples per month, will be sampling at a higher frequency to monitor the status of bloom and will remove caution signs when levels of cyanotoxin are below the action trigger.