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Summertime Algae: How to Prevent and Manage Algae Blooms in Your Pond or Water Garden

by Joe Cadieux on December 27, 2022

Hello all,

Thanks for taking the time to read my articles, I appreciate it.


Summertime algae:

Hot sticky weather is perfect for growing algae.  Whether you own a pond that is 3 acres or a backyard watergarden; without a management plan, summertime blooms can/will be severe. Dense algae can endanger the health of your fish, denigrate the overall water quality, and degrade overall aesthetics of your favorite aquatic system.

Algae, being a photosynthetic organism, excretes oxygen as a waste product during the day.  At night, however, algae consumes oxygen and large blooms can deplete waters that are already starved for DO (dissolved oxygen), as warm water holds much less oxygen then cold water.  Therefore, it is imperative that you keep the water turning this time of year.  Keeping your aerators running and/or your waterfall filter operational into the night will decrease the likelihood of oxygen deprivation and the inevitable fish kill.

OK….. how do we prevent this from becoming an issue?  Maintain your pond!

If you ignored your lawn for a month in the summer, what would it look like?  The same is true for the waters under your care.  Nipping small problems in the bud removes the perils of huge algae blooms.

Nutrient management through a bacteria and enzyme regime directly competes with algae for food and space(Beneficial Bacteria).  Beneficial microbes kickstart the bottom of the food chain and are the crucial start to nutrient sequestration in aquatic systems.

Sometimes things just gotta die….

There are times where you’ve done all you can and you still get algae. Well, then, kill it dead……remorselessly obliterate the offending algal scum using the implements of phycological genocide (in the appropriate doses and active ingredients for your waters). (watergardens)(large non-koi ponds)…… Please read the labels so you do not endanger any non-target organisms (fish, frogs, small children, politicians).

It is always easier and better for your pond, no matter its size, to treat algae blooms when they are small.  All mat-forming algae begins its life on the bottom, so if you see some floating, there is a very good chance that the next generation is on its way behind it. Treating for the floating mats and the next wave will extend the length between treatments and make it more likely that you will be able to maintain your water with the more natural bacteria and enzymes noted above.

Important note:  Algicides also kill beneficial bacteria.  After treating for algae, be sure to increase your first dose of bacteria a couple of days later to bolster the natural recolonization of the bottom of your ecosystem.

So, Long story longer…… CONSTANT VIGILANCE! Summertime blooms are best avoided by keeping watch, and heading them off before they occur.

If you have let your attention wander or conditions are perfect for algae, the resulting large blooms must be dealt with very carefully.  Treating the whole pond can cause the same kind of oxygen deficit as discussed above. Treat half or 1/3 of the pond at a time as algae in its death throws consumes a good deal of DO.  Algae grows very fast and dies just as quickly. The decomposition process consumes adjacent oxygen in the water column.  Planktonic algae (pea soup greenwater) is harder to deal with. Treat with the appropriate dose of algicide or floculate it out of the water column. This is a very delicate problem as algae densities are harder to diagnose and can be just as(or more) severe a problem than the filamentous algae.  Please ask questions in the comments if you need some help.

Please return to my page regularly, as I will be expanding and expounding on these topics in more depth as we go along.

This is a small chunk of a larger conversation, and everybody’s pond is different.  If you need help please comment or give us a call. We can set you up on a program to help make pond maintenance easier.

Thanks so much for taking the time to read…. enjoy the warm weather.


Senior Biologist
CSJ&J Gardens & Midwestponds.com