Chesapeake Bay Coastal Bays Rivers and Streams Watersheds
Maryland Department of Natural Resources
Fixed Station Monthly Monitoring
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Monthly Monitoring Data
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Continuous Monitoring
Water Quality Mapping

Chesapeake Bay Mainstem - MD Mid Bay (CB4.2C)

Map Showing the Location of CB4.2C

Southwest of Tilghman Island

Coordinates (NAD83):
Latitude: 38.6448
Longitude: -76.4177

This station is a mid-channel site located in the mid Chesapeake Bay, southwest of Tilghman Island. The station is located in the mesohaline zone (salinity 5 to 18 ppt) with an approximate depth of 26 meters. Stations in this section of the Bay monitor water quality of the deep trough near the Choptank River.

Current Parameter: Water Clarity (Secchi Depth)

Choose Other Parameters:
Salinity pH Water

The yellow shaded area represents the range of monthly mean values that have occurred from 1985 to 2014. The blue line shows the monthly mean values for each month over that same time period. The red line shows what the current years conditions are and how they compare to the range and the average values we've seen.

2015 Water Clarity (Secchi Depth)
Chesapeake Bay Mainstem / MD Mid Bay (CB4.2C)


Range 1985 to 2014 2015 Mean

Water Clarity (Secchi Depth) (meters)
Chesapeake Bay Mainstem / MD Mid Bay (CB4.2C)
Month Minimum Mean Maximum 2014 2015
January 1.00 1.92 3.20 Not Sampled 1.60
February 0.50 1.96 3.60 1.10 1.00
March 0.40 1.78 3.05 1.00 2.80
April 0.45 1.50 2.50 0.80 2.50
May 0.60 1.57 3.20 0.60 1.30
June 0.65 1.44 2.10 1.20 1.40
July 0.70 1.36 1.85 1.20 1.35
August 1.00 1.56 2.10 1.55  
September 0.70 1.68 2.40 1.80  
October 1.00 1.73 2.70 1.70  
November 1.20 2.06 3.40 1.50  
December 0.60 1.76 4.00 1.40  

*Bottom - "Secchi Disk Was Visible On Bottom":
When the Secchi disk is still visible on the bay floor it means that the water is clear enough for light to penetrate to the depth of the disk, reflect off of the disk, and reach the surface of the water again. Most of the time, this means that there is enough light for submerged aquatic plants to grow to that depth.

NOTE: Results displayed are provisional and have not undergone full Quality Assurance procedures. Although Maryland DNR believes the data presented here are correct, we cannot guarantee their accuracy at this time.

Choose Other Parameters:
Salinity pH Water

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Additional water quality data, including nutrient data, is currently available through the Chesapeake Bay Program Data Hub.

Contact MD DNR's Resource Assessment Service at (410) 260-8630
or by email at

Chesapeake Bay | Coastal Bays | Rivers & Streams | Watersheds

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