Just like any other plant, bay grasses go through photosynthesis, so they need sunlight to grow. This means that the water that bay grasses grow in must be clear enough for the sun’s rays to pass through.

People contribute pollution that can cloud the water and block sunlight from reaching bay grasses. This pollution comes from many sources, including farms, sewage, fertilizer and development.

The Chesapeake Bay watershed stretches across more than 64,000 square miles.

Scientists usually use an electronic dissolved oxygen meter to measure the amount of oxygen in the water.

Scientists use a device called a Secchi disc to measure water clarity. A Secchi disc is a simple, black-and-white circle attached to a rope. The Secchi disc is lowered into the water until it disappears, then pulled up until it can just barely be seen. Scientists note the water line on the rope and measure the distance between the Secchi disc and the water line. The measurement is the water’s clarity: the depth that sunlight is able to penetrate through the water.

Altogether, more than 100,000 streams, creeks and rivers thread through the Chesapeake Bay watershed.

An estuary is a partially enclosed body of water where fresh water from streams and rivers mixes with salt water from the ocean. The Chesapeake Bay is an estuary.

Visit the EPA’s Surf Your Watershed page, where you can enter your zip code to find out what watershed(s) you live in.

Bay grasses are plants that grow underwater in the Chesapeake Bay’s shallows. Bay grasses are also known as submerged aquatic vegetation or SAV.

Global warming has led to sea level rise and increased temperatures in the Chesapeake Bay region and throughout the world. Other possible effects of global warming include habitat loss, increased precipitation and changes in wildlife patterns.