Weeds, Algae & Pond-Scum…. OH MY!

Timing for Fish Stocking – Spring 2019
April 11, 2019

As summer gets started and water temperatures warm, we get lots of calls about different weeds, algae and all sorts of miscellaneous pond scum.  This article is my attempt to address many of these questions and to provide some basic strategy for how to manage these issues in your pond.

Aquatic Weeds

First, let me start by saying that not all aquatic vegetation is bad.  Just because something green is growing in your pond doesn’t necessarily indicate that you have a major problem.  It is generally normal to have something like 15-25% of a pond bottom covered with some sort of vegetation, sometimes less if the pond is deep and has steep drop-offs, sometimes more if the pond is shallow.  Aquatic vegetation provides habitat for fish and for the other pond critters that form the food chain for fish, so some vegetation is a good thing in a fish pond.  The challenge comes when you have “too much of a good thing” and vegetation interferes with your enjoyment of the pond, especially if the pond’s primary purpose isn’t fish but swimming or boating.  If this happens, then active management becomes necessary.

“Know thy weed!”  I cannot stress this enough.  Proper identification of the aquatic plants in your pond is absolutely critical to properly controlling them.  I often get calls with folks describing “seaweed” or “you know, the stringy kind that grows up close to the top”.  Unfortunately, this is not adequate for us to make a recommendation for how to manage the plant.  Different species of plants respond to different types of control and randomly dumping a chemical in your pond and hoping for a good result is not usually a successful strategy.  So, step one is plant identification.

We realize that you are probably not a plant identification expert, so we are always happy to help.  The best method available is for you to send me some photos.  Believe me, they are worth a thousand words.  First take a picture of the pond overall, then a photo of the plants growing in the water.  Next rake out some of the plants and place them on a contrasting surface and take a couple of “detail” photos that show leaves and stems and any flowering structures if they exist.  Keep in mind that there may be multiple species of plants, so try to get them all represented in the pictures.  Once you have pictures, email me the photos (dan@harriettahills.com) .  If one plant in particular is “the problem” make sure you identify which one it is.  Once we know what plants are present, we can develop a strategy to control the problems.

Control can take a number of forms.  Sometimes the best solution is mechanical, like raking or cutting.  Sometimes the solution may be an herbicide, or it could be sunlight reduction with a pond dye or nutrient reduction with aeration and pond bacteria.  Frequently it’s a combination.  Aquatic plants grow for the same reason that plants grow in your lawn:  the combination of water, sunlight and nutrients will always result in something green growing in nature.

 

Algae

Algae come in many species and forms, but the most common types that cause concerns in ponds are grouped as planktonic algae and filamentous algae.  Planktonic algae are single-celled algae that are free-floating in the pond; they cause water to be “cloudy” and in high concentrations can cause water to look like “pea soup”.  Filamentous algae are also sometimes called “mat algae”, growing in colonies or mats that start on the bottom of the pond, clinging to structures like plants.  As the mats mature, they build up gas bubbles that are trapped in the filaments and once there are enough bubbles, the mats will suddenly become buoyant and float to the top of the pond and then drift around, generally becoming an unsightly nuisance.

Just like with rooted pond plants, some amount of algae are important and necessary for a healthy fishery and pond, but when the algae becomes excessive, it can interfere with your enjoyment of the pond.  We know that the combination of water, sunlight and nutrients will result in something green and this includes algae growth.  Here are some steps to manage algae.

  1. Manage nutrient inputs.  Preventing run-off from fertilized lawns or animal pastures is a frequent issue.  Manage waterfowl populations, particularly geese, as they add huge amounts of fertilizer to ponds in the form of droppings.  Don’t blow grass clippings into the pond when mowing or trimming.  Carefully manage fish feeding to avoid uneaten feed.    There are other sources of excess nutrients, so look around carefully or have us come out to assess your situation.
  2. Use Aeration and Pond Bacteria to manage nutrients in the pond. Keeping the pond circulated and oxygenated will help reduce nutrient levels and therefore help reduce algae growth over time.  Beside prevention, this is the single most important management tool to engage for the long-term health of the pond.
  3. Add a pond dye to shade algae and plants. This will slow them down and reduce growth, but it won’t remove a problem that already exists.
  4. Consider using a chemical algaecide. There are a number of quality algaecides available that will provide almost immediate relief for an out-of-control algae situation when properly applied to your pond.  As with any chemical, it is very important to read, understand and then follow the directions when applying algaecide.  Add too little, or in the wrong manner and it won’t effectively control the algae.  Add too much or in the wrong manner and you can kill your fish and have other negative impacts on your pond.  Remember that algaecides are a temporary fix.  You will kill the algae that is present today, but as the algae decays, the nutrients become available to grow a new algae crop again later.  For long-term control, use the first three management tools given above.

 

Pond Scum

Pond Scum is an accumulation of lots of things that float on the surface of the water.  This time of year, the most common concern is from pollen, lots and lots of pollen that blows onto ponds and floats around, frequently causing a thick yellow scum.  This pollen is also joined by fuzz blowing on the wind from all sorts of plants and trees; anything from dandelions to cottonwood trees to willows can all contribute to scum on the surface.  This can also be joined by decaying material floating up from the bottom of the pond.  Your best defense for dealing with pond scum is aeration and pond bacteria.  Circulation by aeration will move the scum materials toward the outside of the pond, where you can remove it if you are ambitious.  The pond bacteria will help your pond digest these nutrients and reduce the unsightliness over time.

 

Just like your lawn, your pond requires some management and maintenance to look the way you want it to.  We are available by phone to help you through the challenges that summer can bring.  Give us a call or email for solid advice and strategies that work to keep your pond healthy and looking good all summer.  If your pond is in Michigan, I am available for pond-side consultations as well as for aeration installation, and application of bacteria, algaecides and herbicides.

I hope this finds you planning a weekend by your pond with a campfire and nature all around.

 

Dan Vogler

President

Harrietta Hills