Monday, January 30, 2023
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Atascadero Lake provides many assets and recreational activities for residents of the City of Atascadero. Following are some interesting facts many people may not know about the Lake!

Q: What is the history and background of Atascadero Lake?

Long before there was an “Atascadero Lake”, the small, shallow basin which was to eventually become the Lake, naturally filled with the winter rains and then, just as naturally, receded during the summer heat. Atascadero “Lake” is actually a pond; a low-lying area fed by rainfall and run-off. Please see this link for information about the Salinan tribe of Native Americans and their connection to Atascadero Lake.

As part of his dream for the Colony of Atascadero beginning in 1913, E.G. Lewis had engineers enlarge the existing natural basin, and then he featured the Lake in his promotions to help draw people to the new Colony. As in the past, Atascadero Lake continues to fill each year during the rainy season and then slowly dries as the summer progresses.

In times of limited rain or drought, the water level in Atascadero Lake is much lower than when we’ve had a good, wet season. Without enough rain to create a significant runoff, the lake doesn’t have a chance to fill to capacity, and then the water level sinks much more rapidly in natural response to the warm and semi-arid climate we normally experience here in Atascadero.

Q: Did you know the size, depth and volume of the lake?

Size: 30.5 Acres
Maximum Depth: 13 Feet
Average Depth: 6.85 Feet
Maximum Volume: 68,100,000 Gallons


During the warm summer months, a common and nearly annual source of concern when the water levels recede is algae blooms. Algae are essential ingredients in a balanced aquatic environment. However, following periods of hot weather, conditions which trigger episodes of rapid algae growth followed by its rapid die-off can occur. The cycle is a natural one that occurs during the hot summer months, and can unfortunately result in unpleasant odors occurring from the decomposing algae. Through the years, there have been various efforts undertaken to help maintain the Lake’s water quality and minimize algae blooms.

In 1962, prior to incorporation of Atascadero as a City, San Luis Obispo County had the bottom of the lake scraped to further enlarge and deepen the basin, and the soil from that sediment removal project was then used to create the island.

The City of Atascadero has a nearby water well which has been used in the past to help supplement water levels in the Lake, but when there’s little rainfall, the shallow well naturally runs low and therefore is of not much use during these periods. The City has also implemented the use of a diverter in Atascadero Creek to send some of the creek’s water flow into the Lake, to assist in keeping the water levels in the Lake at optimal levels. Again, during periods of drought or even just when winter rainfall is low, Atascadero Creek doesn’t run as high and therefore water cannot be diverted from the creek into the lake.

The City of Atascadero has also implemented various aeration efforts through the years, including removing sediment from the lakebed, aeration devices and fountains and an on-going repairs and upgrades to the creek-to-the lake supply pipeline.

To further assist in maintaining an optimum water level and quality, in recent years the Friends of Atascadero Lake (FOAL), a local non-profit group which was formed to help keep the Lake beautiful and inviting, drilled a new well on a nearby property and installed a supplemental pipeline to the Lake, which provides fresh water during the summer months. In 2017, FOAL commissioned an aeration system to promote circulation and oxygenation to the Lake.

Even though algae growth cannot be completely eliminated, the City has employed and continues to explore various methods to address algae growth, and continues our work and partnership with Friends of Atascadero Lake and other members of the community. Addressing water quality and algae blooms in Atascadero Lake has always been and always will be a very important and ongoing effort.

Although the Lake is owned by the City of Atascadero, it is important for the public to know that all projects that are planned to be taken in or near Atascadero Lake are governed and overseen by numerous State and Local Regulatory Agencies (such as Regional and State Water Quality Control Boards, the California Department of Fish and Wildlife, and more.) The regulatory process must be followed and the appropriate permits and approvals must be received from one or more of these entities, before the City of Atascadero can undertake any actions which affect the Lake or its environs.

Q: Where does algae come from?

Our beautiful and very scenic Atascadero Lake contains numerous aquatic plants and naturally occurring algae, which provide filtration and shade and are an essential ingredient in providing a balanced aquatic environment. Unfortunately, hot summer days combined with direct sun and reduced water circulation, can create conditions which trigger certain varieties of algae to grow at an extremely rapid rate. Following periods of hot weather, Atascadero Lake routinely experiences very normal cycles of extreme algae growth, also known as algae blooms.

Q: How do we resolve the algae problem?

Even though this natural algae growth cannot be completely eliminated, the City has employed and continues to explore various methods to address it.  Addressing water quality and algae in Atascadero Lake has always been an important and ongoing effort of the City’s.  We have implemented a long-term algae management plan which involves the use of aquatic pesticides, hydrologic and algae level studies, and biological and botanical resources surveys. The management plan focuses on prevention and provides options for addressing algae blooms that do develop. City staff recently performed preventative measures to prevent massive weed growth that would promote algae in open waters, and we have options to implement other measures if needed to eradicate algae blooms.  The City uses herbicides sparingly and only after other preventative measures are in place.  In addition, the water conditions are monitored, sampled and tested; routinely and as needed. It is important to note that all activities and actions the City undertakes that affect Atascadero Lake comply with various State and local regulatory and licensing agencies, including the Department of Fish and Wildlife and the State Water Resources Control Board.

Category: Parks & Facilities

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