An algae bloom at the Foster City Lagoon may have been “unsightly,” but city officials assure that it is a natural occurrence and not harmful.

Crews worked to remove the dead algae that floated to the water’s surface, according to a city news release.

The bloom was caused by recent warm weather, which resulted in dead algae rising to the surface and floating, causing the water to appear discolored.

While some algae blooms can be harmful, the algae in the lagoon were harmless and limited to small, isolated patches, Foster City public works director Louis Sun said via email.

“These small blooms are unlike larger occurrences in lakes or large bodies of water that can deplete the oxygen levels and kill fish or other wildlife. Though unsightly, the small bloom that occurred in Foster City was entirely organic and harmless,” Sun said.

Public works crews cleaned up the bloom after a few days by netting the algae, rotating the water and adding blue pond dye to the water, which slows down photosynthesis and slows the algae’s growth.

Sun said the lagoon is back to its original state and that staff will continue to monitor its condition.

Questions or comments can be directed to the Public Works Department at 650-286-3270. More information about the lagoon and its levee system are available online.