Text Size: A  A  A

Bay Blog: algae


What do algae blooms mean for water quality?

Welcome to the latest installment of the BayBlog Question of the Week! Each week, we take a question submitted on the Chesapeake Bay Program website or a frequently asked question and answer it here for all to read.

This week’s question comes from Peg: “We have a second home on a creek in Virginia. While there last week, I noticed an unusual quality in the water. The water appeared unusually murky and quiet and there was a large ribbon of a reddish brown color, very distinct, stretching through our cove.  Contrary to normal situations there was a period of time where there were no fish noticeably jumping or swimming and no birds fishing. Could this have been some sort of red tide or algae bloom and what does that mean as far as water quality?”

Each spring and summer in the Chesapeake Bay region, low-oxygen “dead zones” and harmful algae blooms appear in various parts of the Bay and its creeks and rivers. The size and severity of algae blooms and dead zones in the Bay depend on the amount of water that flows into the Bay. That water brings excess nutrients and sediment from the land. Combined with high temperatures, the excess pollutants can fuel the growth of algae blooms and cause the water to become clouded and discolored.

The water condition Peg may have observed is called a mahogany tide, which can cause the water to appear reddish brown. Mahogany tides may also deplete the water of oxygen, which may be why Peg did not see fish in the water as she normally does. Algae blooms make conditions difficult for much of the aquatic life in the Chesapeake Bay. 

Algae blooms can be very detrimental to the health of the Bay. Some are considered harmful algae blooms (HABs) and can be toxic to aquatic life such as fish, oysters and crabs. They can also cause skin irritation or other sickness to people who come into contact with them.

Even if algae blooms aren’t toxic, they can still be harmful to the Bay. When algae blooms get dense enough, they block sunlight from reaching bay grasses growing at the bottom of the Bay. Of course, bay grasses are vital to the Bay's health, so when fewer bay grasses grow, the cycle of poor Bay health continues. When algae blooms die they create more problems, as the decomposition process sucks up most of the oxygen that fish, oysters and crabs needs to survive.

Since algae blooms are fueled by excess nutrients, you can do your part to help prevent algae blooms in your local waterway by taking small steps to decrease polluted runoff. Small steps such as not fertilizing your lawn, picking up your pet's waste and planting more trees in your yard can make a difference.

Do you have a question about the Chesapeake Bay? Ask us and we might choose your question for the next Question of the Week! You can also ask us a question via Twitter by sending a reply to @chesbayprogram! Be sure to follow us there for all the latest in Bay news and events


The ABCs of HABs: How Harmful Algal Blooms Impact the Bay

Algae are a vital component of the Bay's ecosystem—these free-floating plants make up the base of the food chain. Their size ranges from tiny microscopic cells floating in the water column (phytoplankton) to large mats of visible "macroalgae" that grow on bottom sediments. Algae behave much like land plants, soaking up the sun's rays to produce energy while converting carbon dioxide to oxygen during photosynthesis.

However, when algae populations explode to unusually high numbers they create what are called harmful algae blooms (HABs), which can:

  • Block sunlight that is vital for underwater bay grasses.
  • Impede filter-feeders from obtaining food.
  • Produce smelly surface scum.
  • Consume dissolved oxygen when the algae die and decompose.

In addition, certain algae can also produce harmful chemicals that are toxic to humans, wildlife and aquatic life. Fortunately, of the more than 700 species of algae in Chesapeake Bay, less than two percent of them are believed to have the ability to produce toxic substances.

HABs are primarily fueled by excess nutrients (nitrogen and phosphorous) in area waterways, which come from agriculture, air deposition, septic systems and sewage treatment plants, and runoff from lawns, gardens and paved surfaces.

While phytoplankton form the base of the food chain, the amount of nutrients now entering the Bay is overwhelming the system. Oysters and other filter feeders can't consume all the phytoplankton in the water. Unconsumed phytoplankton sink to the bottom of the Bay and are decomposed by bacteria in a process that depletes the water of oxygen. Decomposing phytoplankton, combined with high summer water temperatures, can cause large swaths of the deepest parts of the Bay's mainstem to have little or no oxygen to support fish, crabs and other marine life.

Residents of the Bay watershed can help give the Bay's crabs, fish and other species some relief from HABs by taking simple actions to reduce nutrient pollution, including driving less, upgrading septic systems, picking up pet waste and reducing the use of lawn fertilizers.

Bay Program partners actively monitor the region's waterways for HABs, so that if one occurs the public can be notified to protect human health. Citizens are also asked to keep a watchful eye out for possible HABs and are urged to report suspected HABs to their respective state environmental agency:

  • To report HABs in Maryland call (877) 224-7229.
  • To report HABs in Virginia call (888) 238-6154.

Keywords: algae, phytoplankton
410 Severn Avenue / Suite 112
Annapolis, Maryland 21403
Tel: (800) YOUR-BAY / Fax: (410) 267-5777
Directions to the Bay Program Office
Terms of Use | Privacy Policy
©2012 Chesapeake Bay Program | All Rights Reserved