Algae blooms in Montgomery County

Image of algae in a Montgomery County lake.
August 27, 2013
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In late August, 2013, a bright green scum became visible on the water surfaces at Lake Needwood and Lake Frank. This is the result of a very dense ‘bloom’ of single-celled plants called algae. This particular algae thrives in hot, dry weather and in waters which have high amounts of nutrients (i.e. fertilizers).

According to the Maryland Department of Natural Resources, “Some strains of Microcystis may produce toxins that have been reported to result in health problems to animals that drink the water, and minor skin irritation and gastrointestinal discomfort in humans that come in contact with toxic blooms.”

Montgomery County Parks has posted bright yellow warning signs for visitors to these recreational areas.  Residents should not drink or touch the water, nor swim or wade in areas where this bright blue-green bloom is evident, and should keep children and pets out of these areas. If contact is made, wash off with plenty of fresh water.  The signs are temporary until the algal problem is resolved.

To find out the status of the current bloom and the Parks recreational facilities, contact Parks at 301-495-2595.


Image of a stormwater pond with a severe algal bloom.

A stormwater pond with a large algal bloom.


Algae is a natural part of our ecosystem.

The algae that is the cause of concern in Lake Needwood and Lake Frank is a commonly found species in Montgomery County.  The size of the algae population is typically held in check by natural factors such as temperature, nutrient level (food for algae) and rain levels.  In the summer and early autumn months, especially after minimal rainfall, algae can grow beyond safe levels and can cause the issues we’re finding in the two lakes.

A fact sheet on this type of algae can be found here.


Help prevent future algal blooms

Human activity contributes to the frequency of algal blooms. We can all do our part so as to minimize the occurrence of algal blooms in our local lakes as well as the Chesapeake Bay tributaries.

  • Reduce or eliminate fertilizer usage on your lawns or landscaping.  Fertilizer contains higher levels of nitrogen and phosphorus, which serve as food to algae.  If using fertilizer, follow the guidelines on the Maryland Department of Agriculture’s guide, How to Fertilize Your Lawn Responsibly. For established lawns, only apply in the fall and carefully measure and only apply the amount recommended on the package. For your outdoor plants, try to use ‘organic’ sources like compost that do not wash away as readily as the inorganic sources.
  • Scoop your poop.  Pet waste is another source of nitrogen and phosphorus. Pick up after your pet and dispose of the waste properly.


Stormwater management and algae questions

Stormwater management practices, especially ponds, can occasionally see algae growing on the water, or in rare instances, algal blooms.  This is most common in the summer months.  If you are concerned about the algal level in your stormwater practice, first consider the following questions before taking further steps.

  • Are you sure it’s algae?  Many small surface water plants look similar to algae, such as duckweed.
  • Does your pond have buffer vegetation?  Plants around the edge of ponds and in shallow areas help filter the water of nutrients.
  • Is there a large outside source of nitrogen or phosphorus?  Have you recently fertilized or changed lawn care practices?


Contact the Montgomery County Department of Environmental Protection with further questions about your stormwater management practices at

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