Do you have a question about the Chesapeake Bay? Explore our list of frequently asked questions to learn more about the Bay and its watershed, habitats and wildlife. You can browse the FAQ by category, or explore the answers to some of our most common questions below.
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Oysters prefer brackish and salty water. A salinity range between 10-28 parts per thousand (ppt) provides the best conditions for oysters. Oysters can die if salinity drops below 5 ppt for extended periods of time.
Scientists use a small, long, hand-held device called a refractometer to measure salinity.
The Chesapeake Bay’s overall average salinity ranges from 13-17 parts per thousand (ppt), although salinity in the Bay varies widely depending on location, weather and season.
Fresh water enters the Chesapeake Bay primarily from its rivers and streams. Fresh water also enters via rain, snow and groundwater.
Salt water enters the Chesapeake Bay from the Atlantic Ocean, at the mouth of the Bay near Hampton Roads, Virginia.
In general, the lower Chesapeake Bay is salty and the upper Bay is fresh. Salinity gradually decreases as you move north and increases as you move south.
The Chesapeake Bay’s salinity ranges from fresh water (less than 0.5 parts per thousand) to salt water (25-30 ppt). The Bay's salinity is highest at its mouth, where water from the Atlantic Ocean enters. The water at the head of the Bay is fresh. The water in the middle portion of the Bay is brackish: a mixture of salt and fresh water.
The Chesapeake Bay’s salinity gradually decreases as you move north and increases as you move south. Salinity also varies widely from season to season and from year to year, depending on the amount of fresh water flowing from the Bay’s rivers.
The water at the mouth of the Chesapeake Bay is salty because it is mostly made up of salty water from the ocean. As you move north in the Bay, the water becomes less salty. Most of the Bay is brackish (a mixture of fresh and salty water).
The Chesapeake Bay is saltiest at its mouth, near Hampton Roads, Virginia. This is where salty ocean water comes into the Bay. The Bay’s salinity decreases as you move north.
Salinity is a measure of the amount of dissolved salts in the water. Water can be fresh, salty or brackish (a mixture of salt and fresh water).
Sometimes the Bay’s deeper waters have little or no oxygen while surface waters have more oxygen. This usually happens in summer because of a combination of factors, including temperature, nutrient pollution, the way water flows in the Bay, and the shape of the Bay’s bottom.
Temperature, nutrient pollution, the way water flows in the Bay, and the shape of the Bay’s bottom all interact with each other to affect the amount of oxygen in the water.
Extreme temperatures can have a negative effect on some bay grasses. For example, eelgrass cannot grow in water that is too warm. In 2005, very high temperatures caused large areas of eelgrass in the lower Chesapeake Bay to die. Other species of bay grasses react positively to high temperatures and grow more quickly when the water is warmer.
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