Maryland Department of Natural Resources examined a water sample collected Sunday May 23rd by charter boat operator Captain Jim Brinsfield near the Thomas Point Lighthouse off the mouth of the South River. The surface water in the area was described as reddish-brown. The dinoflagellate Prorocentrum minimum, a Mahogany tide organism known for discoloring Chesapeake Bay waters in the spring, was the dominant algae identified at 14,945 cells per milliliter with the diatom Chaetoceros subtilis also abundant at 11,130 cells per milliliter.

Water quality in the vicinity of Thomas Point lighthouse includes salinity levels tracking lower than average throughout the year at the nearby Kent Point and Bay Bridge long-term Chesapeake Bay monitoring sites. Water temperatures and bottom water dissolved oxygen, however, are above average for the month of May. Water clarity has been below average all year for the Kent Point station and follows a similar pattern at the Bay Bridge, except for May, which was observed to have above average water clarity in the first half of the month.

The continuous water quality monitoring station located at the mouth of the Rhode River southwest of Thomas Point Lighthouse shows data through May 13th with declining dissolved oxygen levels at the site. This downward trend followed an algal bloom on May 8th and 9th as indicated by the chlorophyll levels peaking at > 50 ug chlorophyll a per liter; chlorophyll a is used as an index to algal abundance.