Table VI-2. Summary of Chesapeake Bay water clarity criteria for application to shallow-water 
bay grass designated use habitats. 
Salinity 
Regime 
Water Clarity 
Criteria as 
Percent Light- 
through-Water 
Water Clarity Criteria as Secchi Depth 
Temporal 
Application 
Water Clarity Criteria Application Depths 
0.25 
0.5 
0.75 
1.0 
1.25 
1.5 
1.75 
2.0 
Secchi Depth (meters) for above Criteria Application Depth 
Tidal-fresh 
13 % 
0.2 
0.4 
0.5 
0.7 
0.9 
1.1 
1.2 
1.4 
April 1 - October 31 
Oligohaline 
13% 
0.2 
0.4 
0.5 
0.7 
0.9 
1.1 
1.2 
1.4 
April 1 - October 31 
Mesohaline 
22% 
0.2 
0.5 
0.7 
1.0 
1.2 
1.4 
1.7 
1.9 
April 1 - October 31 
Polyhaline 
22% 
0.2 
0.5 
0.7 
1.0 
1.2 
1.4 
1.7 
1.9 
March 1 - May 31, 
September 1 - November 30 
'Based on application of Equation IV-1, PLW = 100exp(-K d Z), the appropriate PLW criterion value and the selected application 
depth are inserted and the equation is solved for Kj. The generated Kj value is then converted to Secchi depth (in meters) using 
the conversion factor = 1,45/Secchi depth. 
Appendix A and U.S. EPA (2003) for broad and detailed descriptions, respectively, 
of the shallow-water designated use and its boundaries. 
The Chesapeake Bay water clarity criteria should not be applied to a designated use 
or in a period during the year for which they were not derived. The March 1 through 
May 31 and September 1 through November 30 temporal application for the poly¬ 
haline water clarity criteria was originally established for protection of eelgrass 
(Zostera marina) beds (Batiuk et al. 1992). Widgeon grass (Ruppia maritima) co¬ 
occurs with eelgrass in polyhaline habitats. In shallow-water habitats where both 
species currently or historically co-occur 1 , states and other users should assess water 
clarity criteria attainment using a March 1 through November 30 or April 1 through 
October 31 temporal application period. 
When the water clarity criteria were derived, there was an insufficient scientific basis 
for deriving a set of water clarity or related (e.g., total suspended solids) criteria for 
protection of open-water designated use habitats. 
The EPA expects the states to adopt the salinity regime-specific water clarity criteria 
to protect their shallow-water designated uses, presented in Table VI-2. States are 
expected to measure the achievement of the shallow-water designated use at the 
Chesapeake Bay Program segment scale by achieving an established acreage of 
underwater bay grasses, attainment of the applicable water clarity criteria at an 
'Maps of the potential and recent distributions of both species were published by Batiuk et al. (1992); 
see page 125 for eelgrass and page 128 for widgeon grass. Further information on underwater bay grass 
aerial survey findings on the distribution of these two species can also be found at the Virginia Institute 
of Marine Science’s website at http://www.vims.edu/bio/sav. 
chapter vi 
Recommended Implementation Procedures 
