What are water quality standards?
State and Federal laws set standards annually or seasonally to protect a water body, depending on its designated use. These standards are set by first defining the water body’s designated use, then, determining what water quality thresholds must be met in order to support the designated use.
Designated Uses define an intended human and aquatic life objective, use, or goal for a water body. An area's designated use refers to a water body's function – such as fishing or swimming. It takes into account the attainable use of the water body for public water supply, the protection of fish, shellfish, and wildlife on a consumer level, as well for its recreational, agricultural, industrial and navigational purposes.
The Chesapeake Bay tidal waters designated uses, reflect the variety of habitats found throughout the Bay and its tidal tributaries. The Bay's fish, crabs, oysters and underwater grasses are distinguished by natural habitats that differ by salinity and depth and not artificial boundaries. This is why the states try to advocate their protection.These five revised Chesapeake Bay tidal water designated uses more fully reflect the different water resource communities inhabiting them, and the protection of aquatic life in the tidal habitats.
1. Migratory Fish Spawning and Nursery
Migratory fish including striped bass, perch, shad, herring and sturgeon during the late winter/spring spawning and nursery season.
In tidal freshwater to low-salinity habitats. This habitat zone is primarily found in the upper reaches of many Bay tidal rivers and creeks and the upper mainstem Chesapeake Bay.
3. Open-Water Fish and Shellfish
4. Deep-Water Seasonal Fish and Shellfish
5. Deep-Channel Seasonal Refuge
What are “Water Quality Criteria”?
February 1 - May 31
30 day mean of >=5.5 mg liter-¹ in low salinity; 5 mg liter-¹ in high salinity7 day mean of >= 4 mg liter-¹Instantaneous minimum of >= 3.2 mg liter-¹
Deep-Water Seasonal Fish and Shellfish
30 day mean of >= 3 mg liter-¹1 day mean of >= 2.3 mg liter-¹Instantaneous minimum of >= 1.7 mg liter-¹
Deep-Channel Seasonal Refuge
Chlorophyll aMeasurements of chlorophyll a indicate levels of phytoplankton or algal biomass in the water column. Bay chlorophyll a levels should be moderate. Levels that are too high cause harmful algal blooms that lead to poor quality food, shade the light in shallow water habitats. This results in low dissolved oxygen conditions when the algae die off and sink to the bottom.Water Clarity
Underwater grasses are an essential component of the Bay's living resources habitat. Decreased water clarity inhibits the growth of underwater Bay grasses. Increased sediment loads and algal biomass, spurred by excess nutrient inputs to the Bay, will impact water clarity. Bay water quality conditions should have high water clarity to allow sunlight to penetrate, and support underwater grass restoration throughout the Bay's shallow-water habitats.
The criteria involve SAV (Submerged Aquatic Vegetation) restoration goals (acres of standing SAV crop), or measuring water clarity criteria using a Secchi disk technique.
What is a “Restoration Variance”? Why is it necessary?A restoration variance allows dissolved oxygen criteria to slightly exceed the requirement up to 7% in a couple of the deepest areas of the Bay.
This modification to the Bay water quality standards was necessary because in those few deep areas, we may not meet the dissolved oxygen requirements. Even after spending billions of dollars to reduce nitrogen, phosphorus, and sediment pollution to clean up the rest of the Bay, essentially doing everything we know how to do at this time, the deep areas still could not attain the dissolved oxygen standard. This is a better, more protective alternative than lowering the standard based on current understanding. The information will be updated periodically to keep the water quality standard focused on protecting living resources, rather than proposing something less protective. The State is required to review the restoration variances at least every three years (based on EPA regulations), and adjust it accordingly.
Please direct questions or comments concerning Frequently Asked Questions - Chesapeake Bay Water Quality Standards to Matthew Stover at Matthew.Stover@maryland.gov or 410-537-3611.
1800 Washington Boulevard, Baltimore, MD 21230