Pond Algae Update


September 2020

The children’s beach and Ponds 1 and 2 at Esther Simplot Park remain closed due to the presence of algae.

Test results of an algae bloom discovered near the children’s beach swimming area at Esther Simplot Park back on June 18 showed the bacteria is producing toxins that can be harmful to humans. Out of an abundance of caution, Pond 1 (where the children’s beach is located) and Pond 2 will remain closed for the foreseeable future. Both ponds are closed to all forms of recreation for the health and safety of the public, including swimming, wading, boating, paddle boarding and fishing. Boise Parks and Recreation and Public Works teams continue to monitor and test the bloom weekly.

The following is additional information related to the initial bloom discovered in June to help answer some common questions and provide information on the city’s ongoing management of the ponds:

According to water quality experts with the city’s Public Works Department, heavy rain and runoff led to an increase in nutrients in the ponds in June. It only takes a small increase in nutrients (such as phosphorus or nitrogen) to cause cyanobacteria, a type of photosynthetic bacteria, to bloom. These are organisms that occur naturally in Idaho’s lakes, rivers and ponds.

Parks and Recreation team members have implemented measures over the last few years to reduce nutrient runoff into the ponds. In 2019, the city took steps to increase pond circulation through the placement of 46 underwater aerators and increased river inflow to improve circulation and promote pond health. The city worked closely with hydraulic consultants to place the aerators throughout Quinn’s Pond and the Esther Simplot Park water complex.

It is worth noting that during the summer of 2019, there were no pond closures at Esther Simplot Park or nearby Quinn’s Pond and the measures appear to have been successful in promoting pond health. However, the updates were not enough to mitigate the record setting rain and runoff that occurred the past few weeks. The ponds are also directly connected (hydrologically) to the river and during low river flow, there is reduced water into the ponds, reducing circulation. Parks and Recreation staff have taken steps to increase the flow of water through the ponds to help improve water quality.

City of Boise team members will continue to observe and test Pond 1 and 2 at Esther Simplot Park to learn more about the cyanobacteria and implement strategies to mitigate it. We do not have an estimated reopening date for the ponds at this time.

Quinn’s Pond and Veterans Pond remain open for swimming, wading and recreation as test results continue to show that they have not been affected by the cyanobacteria.

If you have any questions or concerns, please contact Boise Parks and Recreation.

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