Mystic — The state Department of Agriculture notified residents Thursday that it will conduct a study next week of how wastewater may affect oysters growing in the Mystic River and Long Island Sound that will include use of a dye that will briefly turn a portion of the river reddish.

The dye is harmless, the agriculture department said in a news release.

The study, from Tuesday to May 21, will track the flow and dispersion of wastewater discharging into the Mystic River and Long Island Sound from the Stonington-Mystic Water Pollution Control Facility, the department said.

Information collected during this study will be used to evaluate the impact of wastewater discharges on shellfish-growing areas in Groton and Stonington, and help scientists determine where shellfish may be safely harvested, the department said.

The dye, called Rhodamine WT, will be released from the Mystic treatment plant beginning Tuesday morning, and will continue for 12 hours until approximately 5:30 p.m. As a result of the dye injection, portions of the Mystic River and Mystic Harbor visible from the shores of Groton and Stonington may turn reddish in color for a brief time.

The study will be conducted by scientists and engineers from the state agriculture department’s Bureau of Aquaculture, the U.S. Environmental Protection Agency’s New England Regional Laboratory, and staff from the U.S. Food and Drug Administration Shellfish Sanitation Program, the agriculture department said.

The Mystic plant recently was upgraded to employ ultraviolet disinfection and a biomagnetic water-clarifier system. Ultraviolet disinfection has proven to be an effective treatment against bacteria and viruses contained in sewage, and does not require the introduction of chemicals into the waters of Long Island Sound, the department said.

The goal of the project is to allow the expansion of existing aquaculture businesses and potential additional cultivation in the river while ensuring the protection of public health. Members of the Noank Aquaculture Cooperative have expressed interest in directly harvesting oysters from the Mystic River, the agriculture department said.

Historically, this portion of the Mystic River has been used as an oyster grow-out area for the cooperative, from which oysters are harvested and relocated to offshore waters for natural cleansing. Because of the proximity of the potential growing area to the treatment plant, a complete sanitary evaluation of the potential growing area is required by the Interstate Shellfish Sanitation Conference‘s National Shellfish Sanitation Program Model Ordinance adopted by the U.S. Food & Drug Administration for interstate shipment of shellfish.

In addition, in order to allow the direct harvest of shellfish from the area, the shellfish authority must document that levels of microbial indicators in the shellfish are suitable for raw consumption. Information collected during this study will be used as part of an ongoing evaluation of the Mystic River and Mystic Harbor for a potential seasonal upgrade for direct harvest, the department said.