water quality criteria. Therefore, the report’s recommendations for the allowable use 
of midchannel data should be used with appropriate caution only in the absence of 
shallow-water quality monitoring data. 
Estimating Areas Characterized by Midchannel Stations. It is possible to 
determine a distance from a specific midchannel station for which it is appropriate 
to use the midchannel distance to characterize the shallow-water environment. 
Results revealed that the underwater bay grass habitat quality conditions are indis¬ 
tinguishable between shallow-water and adjacent midchannel stations 90 percent of 
the time, when station pairs were separated by less than two kilometers. This radius 
differs on a site-by-site basis (see Batiuk et al. 2000, Chapter IX, Table IX-3 and 
figures IX-4a through IX-4o). Decisions to use midchannel data to characterize 
shallow-water conditions should be made on a site-by-site, tributary-by-tributary 
basis. Karrh (1999) provides detailed illustrations of estimated distances from 
midchannel monitoring stations to the farthest point where the shallow- 
water/midchannel data are comparable. 
River Input and Flow Considerations 
States responsible for measuring water clarity/shallow-water bay grass designated 
use attainment near the fall-lines of where major free flowing rivers enter tidal 
waters should recognize the strong influences of intra- and interannual flows on 
conditions in the shallow-water habitats. The quality of the waters entering the tidal- 
fresh reaches of these rivers is greatly influenced by flow levels. The decadal scale 
record of underwater bay grasses distributions and concurrent water quality moni¬ 
toring data provides the states and other users with a wealth of information from 
which to gather information on the relative influence of flow conditions on observed 
attainment. In the case of water clarity attainment and restoration of underwater 
grasses, the EPA recommends recognition within states’ water quality standards of 
the influence of river flow conditions on water clarity and underwater bay grasses 
(through chlorophyll a and suspended solids contributions to reduced light penetra¬ 
tion) particularly for the tidal reaches just below the major river fall lines. 
Management actions directed toward attaining the water clarity criteria and shallow- 
water bay grass designated use attainment in these tidal reaches should also reflect 
the long-term flow conditions and influences on local shallow-water habitat quality. 
CHLOROPHYLL A CRITERIA ASSESSMENT 
'Recommended' Level of Monitoring 
Monitoring for chlorophyll a criteria assessment requires a significant amount of 
spatially and temporally intensive data. Algal blooms tend to occur sporadically and 
in patches throughout the Chesapeake Bay. The severe nature of blooms, associated 
dissolved oxygen extremes and associated releases of toxins are what cause ecolog¬ 
ical impacts. 
chapter vi • Recommended Implementation Procedures 
