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1. Let me ask about the foam first. What causes foam to appear on lakes, rivers, and streams?

As with most liquids, water molecules are normally attracted to each other. This attraction creates tension at the surface of the water, often referred to as a thin "skin," which allows some insects to glide across it.  When leaves, twigs or other organic substances fall into water and begin decaying, they release compounds known as surfactants.  This interaction breaks the surface tension, which in turn allows air to more easily mix with water and creates bubbles. These bubbles congregate as natural foam.  However, not all foam is natural. Certain man-made products, including detergents, can cause foam that is similar in appearance, but may be harmful to fish and other aquatic life.

2. OK, good info. When am I most likely to see natural foam on a waterbody?

Great question.  Foam can form on our water bodies a number of different ways:

• On a windy day, because foam occurs when a breeze agitates the water to form bubbles. 
• During the fall when trees drop their leaves and aquatic plants begin to die back and decompose.
• Throughout the spring as plants lose their buds.
• When the outdoor temperature rises, because heat accelerates plant decay, which releases the organic substances that contribute to foam.
• During soil erosion events or from human activities, such as gravel washing.

3. Well, that makes sense. But is foam harmful?

Foam is usually harmless. In fact, only 1 percent of the foam you see on a waterbody is the actual foaming agent; the rest is air and water.  However, excess foam is sometimes the result of too much phosphorus in the water.  Although phosphorus is an important plant nutrient, it is not found abundantly in nature and too much of it is indicative of pollution from human activities.  Excessive phosphorous can result in nuisance algae blooms, fish kills due to low dissolved oxygen from decomposition processes, and irregularities with the water's taste and odor.

4. Natural and unnatural foam: got it. How can I tell what kind of foam it is?

Although it's difficult to know for sure, foam from various sources can have different characteristics.

Natural foam usually:

• appears as light tan or brown in color, but may be white;
• smells earthy, fishy or has fresh cut grass odor;
• can occur over large areas and accumulate in large amounts, especially on windward shores, in coves and eddies; and
• dissipates fairly quickly, except when agitated (as in high wind conditions).

Unnatural foam from human activity usually:

• appears white in color;
• gives off a fragrant, perfumed or soapy odor; and

usually occurs over small area, localized near a source of discharge.

5. What should I do if I suspect a waterbody's foam is the result of a chemical release or spill?

If you suspect foam to be from unnatural causes, call York County’s Environmental Compliance Department.  The telephone number is 803.909.7250.  The sooner you call: the better.  If an illegal discharge is the cause, we need to know as much information as possible so we can get to it fast to minimize the danger to people and the environment.  

6. Wow… I’m learning a lot! Now that I know about foam, what causes surface scum on a lake?

Scum, an oily film, or yellow-green dust on the surface of a lake makes it look contaminated but, in general, nothing is wrong.  In fact, something natural is probably occurring.  An oily film in midsummer is most likely caused by insect cases that become concentrated along the shore by wind after a hatch. Insects can hatch any time from early spring into September. As the cases decompose, they sometimes give off an oily film. Yellow-green dust floating on the surface in late spring and early summer is pollen from nearby pine trees. In contrast, an algal bloom is green to blue-green, might look soupy, and can form thick, slimy looking surface scum.

7. But why does the water quality of our lake seem to get worse throughout the summer?

First of all, it’s never just one reason. Many factors, including human activity in the watershed, interact to affect the water quality of a lake.  Just as fertilizing a lawn promotes growth, nutrients seeping into a lake increase aquatic plant growth rates.  Agriculture and communities in the watershed may inadvertently add nutrients to the lake through stormwater runoff and over spraying.  Normally lawn and agricultural fertilizers are not innately harmful.  However, excess fertilizer can cause algae to "bloom" which, in turn, decreases light for other plants and animals.  Water quality may worsen at the peak of the growing season when sunlight and nutrients are plentiful.  Other sources which cause water quality degradation come from erosion and sediment washing in from disturbed shorelines or construction sites.  The transported sediment contributes additional nutrients to the water.  All that washed in sediment is what causes muddy water. Development on a lake shore usually means changes in the shoreline plant community (i.e., cultivated grass replaces bulrush). Nutrients and sediments wash into the water more readily without the natural filtering system.