Algae blooms at Barrett and other lakes

[Gotfish?]

Right now, Barrett is experiencing a severe algae bloom. While living algae produces oxygen, dying algae consumes oxygen and that makes fish lethargic and can even cause death with threadfin shad being the most sensitive species to environmental stress. Shad consume some algae (they are filter feeders) but not enough to completely prevent blooms. There are several types of bacteria that can cause blooms, including blooms that float on the surface and blooms that are toxic. If you are in a spot where the water smells, that is sure sign there is algae die off and the fishing will be very poor. But algae die off is not always accompanied by a smell.

Excess nutrients (especially phosphorous) cause the algae overgrowth. This can come from agriculture, cows (manure) or soil run off, especially where there were wildfires. There is some but not a lot of grazing and agriculture in the Barrett watershed but that area is prone to wildfires.

Algae blooms are self limiting in that when algae die, they then sink to the bottom and become sediment and that ties up the phosphorous. Overgrowth of algae will block sunlight to the deeper levels, causing more die off. So in many lakes, blooms will come and go over a season. If the lake level is dropping (as Barrett is now), that will stir up sediment near the shoreline and put phosphorous back into the lake so we may see algae blooms over most of the remaining season. Typically, algae blooms are worst with higher water temperature and Barrett is just warming up for the season. Algae blooms are usually least in the morning and worst in the afternoon.

Cooler weather stops the blooms too. Algae blooms are not limited to Barrett in San Diego County. I have seen pea green water in Hodges and Lower Otay too. They are not limited to fresh water either, harmful blooms have been seen in saltwater too.

On Google maps, Barrett is markedly greener than the other lakes: https://www.google.com/maps/place/Barre ... FQAw%3D%3D.

A 2005 report on Barrett and other watersheds is at https://www.sandiego.gov/sites/default/ ... hap1_2.pdf .