Why Does the Water Look Like That?

Click on the title that best describes what you are seeing on the water. You'll be taken to the full description and analysis.

Looks like:

Murky, Green Colored Water

Description: Murky, green to blue green-colored water, possibly scum, that looks like blue-green paint on the windward shore, unpleasant odor.

Analysis: Algal Bloom. Algae are microscopic plants that are natural components of lakes. When very high phosphorus concentrations occur, one species of algae will out-compete the others and become so abundant that the water becomes murky.

Yellow-Green Dust

Description: Yellow-green dust on the lake in early summer. (late May-June)

Analysis: Pollen from nearby pine trees. The pollen might look similar to algae, but pollen is yellow-green and dust-like and floats mainly on the surface. (An algal bloom is green to blue-green). Over time the pollen will become water logged and sink from sight. Pollen does not have a serious effect on water quality.

Dark Cloud or Oily Sheen

Description: Dark cloud in the water accompanied by an oily sheen.

Analysis: The cloud is probably insect cases left behind from a hatch of aquatic insects; the insects hatch any time from ice-out to September. The wind often concentrates the cases along the shore and, as they decompose, an oily film sometimes forms on the water surface.

Green Cotton Candy

Description: Green, cotton candy-like clouds floating in shallow waters.

Analysis: Filamentous algae are common in many lakes and may not indicate a water quality problem. These clouds usually appear after heavy run-off in the spring or following a long, hot spell in the summer.

However, concentrations of this form of algae only in specific areas may indicate a local pollution source, such as a contaminated stream or failing septic system. If a lake develops this type of algae around the entire shoreline, it may be the first indication of a phosphorus problem in the entire lake.


Description: Foam "soap suds" on the surface or along the shore.

Analysis: Foam along the shore probably does not indicate pollution from laundry waste. Virtually all detergents today are a biodegradable form which is easily broken down by bacteria. Most foam is natural.

Foam is created when the surface tension of water is reduced and air is mixed in, causing bubbles. Many natural organic compounds will reduce surface tension, including those from decomposing algae and fish. In a lake, these organic compounds are mixed with air by wind and currents to produce foam.

Large quantities of foam are often found on windward shores, coves and in eddies. Natural foam has a somewhat earthy or fishy aroma. Detergent foam, in contrast, will have a noticeable perfume smell.

The text on this page is from pp 16-17 ("Unidentified Floating Objects") of "The Lake Book -- Actions You Can Take to Protect Your Lake". Published by the Maine Congress of Lake Associations (out of print).