Originally Posted By: Bill Cody
It looks to me like you have a classic, whopper bloom of bluegreen algae aka Cyanobacteria. They grow well in mid-summer in very nutrient enriched, phosphorus laden water. When the bluegreen bloom is comprised of species on top, they often contain toxins in the cells which are released when the cells die, are killed and then breakdown -decompose. One of the common toxins is microcystin. When the cells age and die the color often changes from green to bluegreen.

To check if it is one of the harmful blugreen algae, collect some 1/2 full in a water bottle and cap it. Allow it to sit capped for a couple hours, then open it, and lightly smell the air inside the bottle. If the odor is offensive, musty, moldy, etc then you have one of the harmful bluegreens. Do not let your dog get in the water and lick the algae off its body. This stuff when ingested can be really harmful to dogs.

When the bloom is this intense you are close to having a fish kill when there are several cloudy days, and or it all dies at once and all the dead material consumes lots of oxygen. In mid-summer when the water is 'hot' it is not able to 'hold' much oxygen compared to colder water, thus DO can get consumed rapidly.



Thank you for taking a look and the information. I'll try the bottle test in a little while when we go feed the ducks and fish. Interesting about the dog issue, although no dogs here at the moment. History is pond was built around 1994, has lots of trees close and sure to be plenty of decaying leaves for nutrients you mentioned.