This is the fourth report of the 2001 season.

Pfiesteria and other algae.
Water samples have been collected since January and surveyed for Pfiesteria species (Pfiesteria piscicida and Pfiesteria shumwayae) using genetic probes developed by Dr. David Oldach of the University of Maryland Biotechnology Institute.  Between January 8 and July 5, 2001, 276 water samples were collected from tributaries of Maryland's Chesapeake and Coastal Bays and tested for Pfiesteria.  Seven samples have tested positive for Pfiesteria species (Table 1).  They were collected from the Pocomoke River, Transquaking River, Pokata Creek, Manokin River in the Chesapeake Bay watershed and Newport Bay on the Coastal Bays.  Genetic probes provide information on the presence or absence of Pfiesteria in the water column but do not tell us about its toxicity.  Because no unusual fish behavior has been observed and fish collected at these locations appeared healthy, these Pfiesteria populations are assumed to be in a non-toxic state.

Table 1. Locations of positive Pfiesteria samples out of 276 samples collected between January 8 and July 5, 2001.

Fish and fish health.
Between June 1^st and July 13^th, there were twenty six investigations of dead fish reported in tidewater areas and investigated by Maryland Department of the Environment and Maryland Department of Natural Resources (Table 2). Most of the investigations involving less than 100 fish appear to be related to fishing discards and none of the sites have been associated with Pfiesteria activity.

Table 2. Investigations regarding dead fish, June 1 to July 13, 2001.

There were three fish kills and three fish health investigations in the tidewaters of the Chesapeake Bay during the week of July 9-13.  A fish kill involving approximately 1,000 fish downstream of Breton Bay on the Potomac River was investigated  July 11. The tentative conclusion is that low dissolved oxygen as a result of an algal bloom resulted in the fish kill and precipitated the appearance of the sulfur bacteria. Water samples collected July 12^th at the site of the kill were negative for the presence of Pfiesteria.  There was another investigation that revealed that 256 menhaden were stranded at low tide and a third investigation in Calvert County.  The third investigation involved about 100 old, dead fish that may have been related to  reports of fish kills caused by low dissolved oxygen last week.

Updating information on the fish kills identified in the July 3^rd report, water samples collected at widely reported fish kills in the vicinity of Herring Bay and Rockhold Creek during the last week of June and first week of July showed no evidence of Pfiesteria. The appearance of many small kills may actually have resulted from fish trapped in a commercial net dying and then being discarded.  Low dissolved oxygen conditions in these areas were reported in initial investigations.  Low oxygen levels may have resulted from the oxygen demands from a bloom of Gyrodinium estuariale, a small dinoflagellate species in the plankton or possibly from a wind driven intrusion of deep anoxic bottom water into shallows in the Bay.

Over 55,000 fish have been collected during fish health monitoring on the Chesapeake and Coastal Bays since June. Between June 25^th through July 1^st there were 30,270 fish collected during routine sampling and less than 0.1 % of the fish showed any form of anomaly.

A reminder - please report fish kills, sick fish or fish with lesions to the Maryland Fish Health Hotline at 1-888-584-3110.

Water quality conditions.
Rainfall during June and early July has generated a return to average flow conditions into the Bay after a period of below average levels earlier in the year. Due to the amount of precipitation, the salinity levels in most of the tributaries of the Bay have remained stable or shown only slight increases and are within normal ranges.  As the summer progresses, the water temperatures in the Bay and its tributaries are steadily increasing while dissolved oxygen levels are generally decreasing.  By July 2^nd, the temperature in the Pocomoke was around 28°C and the dissolved oxygen levels had declined this month but are within normal ranges.  Dissolved oxygen levels in the Chicamacomico River increased from June 18^th to July 3^rd; however these levels are still fairly low at around 4 mg O2/L.  In the Manokin River, water temperatures are around 29°C, which is slightly higher than normal and dissolved oxygen levels at several sites are less than optimal and measuring near 3 mg O2/L. At most other monitoring sites on the Coastal and Chesapeake Bay tributaries, dissolved oxygen levels are above 5 mg O2/L and other water quality conditions have been within the ranges observed between 1997 and 2000.

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