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May 23, 2002
Mahogany tide found in Upper Western Shore Waters.

Magothy River
Mahogany tide resulting from the bloom of the organism Prorocentrum minimum was observed on May 15, 2002 on the Magothy River during routine monitoring work by Maryland DNR. A sample collected at the mouth of Cattail Creek, a tributary of the Magothy River, had concentrations of 200,000 cells/ml, placing it as the highest density observed in the state this year and among samples with the greatest densities observed in the past 20 years.

Other Chesapeake Bay regions
Mahogany tide has been observed in the middle western shore of Chesapeake Bay since at least April 17th when bloom concentrations of Prorocentrum were found in Baltimore Harbor waters (see graph below of all samples in Maryland where Prorocentrum was found this year). Several samples from the Patapsco and Severn Rivers have shown significant bloom densities this spring. The appearance of higher Prorocentrum bloom concentrations may be linked to the weather effects on Bay conditions initiated by the brief hot spell in early April. Similar events occurred in 2000 when air and water temperatures rose rapidly in spring and significant bloom densities of Prorocentrum followed.

Concentrations of Prorocentrum minimum in 2002.

Largest historical Prorocentrum minimum bloom samples,State monitoring program samples or samples in response to water quality complaint calls, 1982-2002.
Date Location Cells per milliliter
03/02/82 Wicomico River (Potomac)/St. Catherine Sound 841,445
08/15/89 Patuxent River 680, 210
05/29/86 Love Point Chesapeake Bay  
05/15/02 Magothy River 200,000
01/01/83 Middle River, Darkhead Creek 178,860
04/26/00 Middle Chesapeake Bay MCB4.1C 152, 823
09/21/94 Patapsco River/Baltimore Harbor 152,375
01/07/91 West River 126,286
12/03/95 Bear Creek/Chink Creek 117, 072
05/08/00 Ragged Point/Potomac River 105,066
05/09/00 Middle Chesapeake Bay 89,586
05/09/00 Middle Chesapeake Bay 74, 435