The Good, the Bad and the Algae

While they might sound like something pretty and delicate, algae blooms are not sweet smelling flowers that blossom in the Chesapeake Bay. In fact they have much to do with the nature of algae (plural, pronounced AL-jee) and the way people use the land around them.

What Are Algae?
Algae are primitive, non-flowering plants that use a process known as photosynthesis to convert sunlight, water, carbon dioxide and nutrients into food. Most algae contain chlorophyll, the same green pigment used by plants, such as grass, to perform photosynthesis.

Photo of an algae bloom in the Lower Sassafras River in July 2003Macroalgae include seaweed and the slimy, green, hair-like stuff that grows on rocks and the sides of aquariums. Microalgae are too small to be seen without a microscope. Most are phytoplankton, single-celled organisms that live suspended in the waters of oceans, bays, rivers and ponds all over the planet. When abundant they give water a color, usually green but sometimes red or brown.

What Are Algae Blooms?
When nutrients are present in excessive amounts, algae grow rapidly. Their numbers can double in a day. Population explosions of algae are known as blooms.

Because different species thrive as waters vary from warm to cold and fresh to salty, algae blooms occur throughout the Bay and throughout the year. However most blooms appear in summer, when sunlight and nutrients are plentiful.

Depending on the species, blooms can form scum, clumps or mats that float near the surface or grow on the bottom. Blooms in the Chesapeake are most often greenish, red or brown.

How Are Blooms Harmful?
While higher organisms -- such as zooplankton, clams, oysters, minnows and menhaden -- eat algae, blooms provide a large surplus of food. Some species low in nutritional value can weaken the organisms that eat them. When algae die, they sink to the bottom. Their decomposition uses more oxygen than they produced when living. The grim result is that blooms rob water of the dissolved oxygen that fish, shellfish and other aquatic creatures need to survive. Blooms block the sunlight needed by bay grasses, which produce oxygen and provide habitats for fish and shellfish. Some blooms produce poisonous substances called toxins. Toxins can weaken or kill fish, harm land animals that drink contaminated water, and cause skin irritations and stomach problems in humans.

How Can We Control Blooms?
Excessive nutrients, mainly nitrogen and phosphorous, cause algae blooms. Though blooms occur naturally when rain and melting snow wash nutrients from the land, today's extraordinary problems are manmade.

Upgrading sewage treatment plants to remove more nitrogen will help. Maryland currently plans to improve 66 large plants. Using fertilizers more carefully on farmland and in our yards will also reduce nutrient pollution.

Restoring forests and wetlands is another way to reduce the flow of nutrients into waterways. The trees and vegetation soak up nutrients much like a sponge, acting as nutrient-storage devices. Planting forested or vegetative buffers along waterways also helps slow runoff, allowing more nutrient-laden water to filter through the ground. Restoring populations of algae-eating organisms, particularly oysters and menhaden, is yet another important way to counteract algae blooms in the Chesapeake.

So there you have it: The good, the bad and the ALGAE!

For more on algae blooms, visit the DNR website at

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