The goal of the Chesapeake restoration effort is a clean Bay—one that meets its water quality standards.

For years, though, the Bay has had water quality standards that differed between the states and were neither attainable, nor protective of the creatures living in it.

In recent years, scientists and state and federal officials have worked to develop new water quality criteria for the Chesapeake that are designed to ensure that different types of fish, shellfish, underwater grasses and other organisms have the water conditions they need in the right places, and at the right time of the year.

The new approach divides the Bay into five different habitat zones—or designated uses—and establishes measurable water quality criteria (for dissolved oxygen, water clarity and chlorophyll a) needed by the species that live in each zone.

The designated uses and criteria are in the process of being adopted as enforceable state water quality standards. They will replace existing water quality standards, which are much less specific or are not attainable in some places while not adequately protective in others.

For example, the dissolved oxygen standard for most of the Bay today is 5 milligrams of oxygen per liter of water. During the summer, the deep waters of the Bay naturally have low levels of oxygen, although increased nutrients have considerably worsened the problem. Even under pristine conditions, those areas would likely have never attained a 5 mg/l dissolved oxygen standard.

At the same time, 5 mg/l is not protective enough for some fish, especially eggs, larvae and juveniles, in certain areas. Also, at present there is no standard for water clarity, which is critical to protect underwater grass beds that provide essential habitat for fish and food for waterfowl.

The resulting designated uses and criteria, based on decades of research on the Bay, are among the most complex in the nation. Achieving the new state water quality standards that will be based upon them would meet the legal requirements of the Clean Water Act, and be considered a clean, restored Bay.

The nutrient and sediment reduction goals are the estimates of what levels of effort it will take to meet the new standards. But ultimately, it is the actual measured attainment of the water quality standards in the Bay and its tidal waters that is required. The nutrient and sediment reductions are only estimates of what it takes to meet the standards, and may be revised if necessary.

Here’s a look at the new designated uses and water quality criteria that apply to each:

Migratory Fish Spawning & Nursery Use: Protects migratory finfish from late winter through the spring spawning and nursery season in tidal freshwater to low-salinity habitats. Located primarily in the upper reaches of many Bay tidal rivers and creeks and the upper mainstem Bay, this use will help species such as striped bass, perch, shad and herring.

Applicable Bay Water Quality Criteria:

Dissolved oxygen: 6 milligrams per liter averaged over 7 days with a 5 mg/l 1-day minimum February through May. From June through January, the open water criteria apply.

Chlorophyll a: The criteria recommend chlorophyll a concentrations (a measure of algae density) for different salinities that would protect localized algal-related problems.

Shallow Water – Bay Grass Use: Protects underwater grasses and the many fish and crab species that depend on the shallow water habitat they provide, including largemouth bass, speckled seatrout and blue crabs. The depth at which the designated use applies varies between one-half meter and 2 meters, depending on the depth at which grasses have been observed in the past, either through monitoring programs or historic aerial photos. Some small areas, such as blackwater rivers, are excluded because they never contained suitable habitat.

Applicable Bay Water Quality Criteria:

Water clarity: At least 13 percent of the light striking the surface must reach plants on the bottom in low-salinity waters, and at least 22 percent of the light hitting the surface in high-salinity water must hit the bottom. Also, tidal river and mainstem Chesapeake segments have specific acreage restoration goals for Bay grasses.

Open Water Fish & Shellfish Use: Includes all surface-water habitats in tidal creeks, rivers, embayments and the mainstem Bay and is intended to protect diverse populations of sportfish, including striped bass, bluefish, mackerel and seatrout, as well as important bait fish such as menhaden and silversides.

Applicable Bay Water Quality Criteria:

Dissolved oxygen: 5.5 mg/l as a 30-day average in tidal freshwater habitats and 5 mg/l as a 30-day average in other areas, with a 7-day average of 4 mg/l & an instantaneous minimum of at least 3.2 mg/l.

Chlorophyll a: The criteria recommend chlorophyll a concentrations (a measure of algae density) for different salinities that would prevent localized algal-related problems.

Deep Water Seasonal Fish & Shellfish Use: Designed to protect the deeper transitional water column and bottom habitats between the well-mixed surface waters and the very deep channels. This use protects many bottom-feeding fish—such as spot, croaker and flounder—as well as crabs and oysters, as well as other important species such as the bay anchovy.

Applicable Bay Water Quality Criteria:

Dissolved oxygen: 3 mg/l as a 30-day average, with a 1-day average of 2.3 mg/l and an instantaneous minimum of 1.7 mg/ from June through September. From October through May, the open water dissolved oxygen criteria applies.

Deep Channel Seasonal Refuge Use: Designed to protect bottom sediment-dwelling worms and small clams that bottom-feeding fish and crabs consume in the very deep channels. Low dissolved oxygen conditions prevail in the deepest portions of this habitat zone, and it will naturally have very low oxygen during the summer.

Applicable Bay Water Quality Criteria:

Dissolved oxygen: 1 mg/l minimum June through September. From October through May, the open water dissolved oxygen criteria would apply.