Prevention of string algae!

Asked March 26, 2014, 4:36 PM EDT

Late last summer our pond developed abundant string algae.......first time in 40 years. We removed as much as possible by rake and now need to know the best chemical treatment for prevention. The pond contains many pond turtles, frogs, and some sunfish and catfish. Please advise the best and safest chemical to use as well as quantity and optimal time of application---now when surface water is flowing in and out---or waiting until pond water is still. Thanking you in advance.

Montgomery County Pennsylvania

1 Response

The first step in addressing an algae or aquatic plant problem is identifying what organisms you have. Your description and the time of year suggest filamentous algae, a category which includes many different species of organisms (sample picture should be linked below). Does that picture look like what you experienced? If not, do you have any pictures you could post or email?

Beyond the type of organisms, most algae and plant problems originate from too many nutrients (such as phosphate and nitrate). Controlling nutrients is the best way to prevent algal blooms. What type of land use is happening around the pond? Any fertilizer application? Is there a buffer of vegetation, or lawn up to the shore? Any geese? A failing septic system? Did anything about nearby land use change last year?

Make sure material from raking is taken away from the pond so that algal cells and the nutrients they release as they decompose are not released back to the pond. Over the years has there been other vegetation in the pond such as submerged plants?

Once I know more about your pond I can give some information on prevention and treatment options. These may include treatments with natural materials, grazing fish, or herbicides. Herbicides are for treatment rather than prevention and usually have to be used repeatedly, so they should be a last resort. Herbicides must be applied based on the species to be controlled, sensitivity of other species present, and the pond volume and flow characteristics. Herbicide application in Pennsylvania requires a permit and must be done in stages to prevent rapid decomposition and a loss of oxygen in the pond that would harm other organisms.