Until 1993, Block Island had not been included in the statewide surveillance program because it lacks Culiseta melanura larval habitat and, given the logistical problems and costs, scarce state resources had been devoted to higher risk areas on the mainland. A September 1993 human death from EEE that was most likely contracted on the island prompted the Mosquito Abatement Coordination (MAC) Office to begin a disease surveillance program and to conduct other mosquito-related projects on Block Island.

1994 trapping data indicated that some 45% of the adult mosquito population was comprised of the three saltmarsh Aedes species common to Rhode Island. A 1994 survey of saltmarsh larval habitats revealed that all of the saltmarsh Aedes were developing in three marshes. Given that the marshes are relatively small, a major reduction in mosquito production is feasible. A major reduction can translate into a significant reduction in the EEE risk on the island.

The three marshes, named Cormorant Cove, Mosquito Beach, and Andy's Way, border the Great Salt Pond. Plans for appropriate mosquito management strategies for each marsh are currently being finalized. Based on 1995 larval surveys and larval habitat assessment, the recommendation for the Andy's Way marsh will probably entail annual monitoring and spot larvicide treatments by hand. The recommendation for the Cormorant Cove marsh will involve minor ditch maintenance, and annual monitoring for larvae and spot larviciding by hand as needed. The Mosquito Beach marsh harbored the bulk (probably in excess of 95 %) of the saltmarsh mosquitoes produced on the island in 1995, and hence is receiving the most attention by the MAC Office.

The Mosquito Beach marsh is approximately 3.6 acres, measuring 200 ft. by 780 ft. One of the long sides is a dune/berm bordering the Great Salt Pond and the other long side borders upland. A principally functional mosquito ditch spans some 700 ft. through the center of the rectangle. It has evidently received no (or minimal) maintenance since it was dug in the late 1930's or early 1940's. In all likelihood, two or three ditches were cut through the berm perpendicular to the main ditch to drain the marsh. Three breaks in the berm have partially filled in but permit the highest tides (only several days per month) to flood the marsh. This situation results in tidal water remaining trapped over an extensive portion of the marsh for two or more weeks. It is ideal larval habitat and poor fish habitat.

The OMWM system being designed for this marsh is intended to reduce the extent of trapped water and enhance fish predation. Briefly, the plan envisioned includes cleaning and deepening the existing ditch, deepening one existing pool, creating another pool, and lowering two or three of the breaks in the berm. The renovated ditch will provide predatory fish greater access to larvae and serve as a fish reservoir. Pools located at each end of the ditch will serve as additional fish refuge during periods of lowest water levels. Lowering breaks in the berm will increase the frequency of flooding and decrease the extent of trapped water. The former will result in increasing fish's access to the marsh from the Great Salt Pond and improving the water quality via more frequent turnover. The reduced trapped water zone will be much more proximal to the ditch, enhancing predation. It is anticipated that stones will line the deepened breaks to serve as erosion control. Given the small size of the breaks, only minimal annual maintenance to clear (potential) sedimentation (by hand) is anticipated.

During the 1995 summer, 3,030 elevational data points were recorded from the Mosquito Beach marsh. (A similar number of data points were also accrued from the Cormorant Cove marsh.) Lateral point locations were chosen based on a combination of a grid system (created with stakes, strings, flags, and tape measures) and the location of pertinent features (ditches, depressions, berms, etc.). The elevational data were acquired via a Nikon electronic level and direct reading rod. This system proved to be highly precise (measurements were recorded to the nearest .01 ft.), efficient, and rapid.

Maps of the Mosquito Beach marsh are currently being developed with a GIS system. They will depict contours, vegetation zones, and several water regimes. The latter set will depict the current extent of trapped water and depict reduced trapped water zones that would result from deepening the breaks in the berm to various levels. Maps will be printed on translucent Mylar at a scale of 1 inch to 20 ft. and overlaid on a black and white aerial photograph of the same scale. The unusually detailed maps will enable a team of marsh ecologists to fine-tune the design and aid in predicting the impacts on marsh flora and fauna following OMWM conversion. The maps will also enhance understanding of the plans and the processes by the concerned environmental and conservation groups and agencies.

This project has been supported from a grant jointly funded by the Town of New Shoreham (Block Island), the EPA's Narragansett Bay Project, and the R.I. Dept. of Environmental Management's Mosquito Abatement Grant program. Should some version of the OMWM design be approved by all concerned parties, joint funding for construction costs will be sought from state, federal, and town sources.