Several Island estuaries have been identified as undergoing anoxic events in the last week. Anoxia occurs when large amounts of decaying plant material such as sea lettuce use up the oxygen in the water. The water turns milky white or cloudy green and gives off a rotten egg smell. The lack of oxygen can also lead to the death of fish and shellfish that are unable to avoid the area.
Cindy Crane, surface water biologist with the Department of Environment, Energy and Forestry, says the areas affected include the Southwest River upstream of Long River, the upper Hunter River between Rusticoville and New Glasgow, the Wheatley River in the Oyster Bed area, and the Montague River near Dewar’s Point. She said anoxic events are known to last from several days to a week or more, depending on weather conditions and prevailing tides.
Anoxic events typically happen between mid-July and mid-August, in the shallow upper reaches of bays and estuaries where there is low water flow. Ms. Crane said north shore estuaries are more susceptible to anoxic events than south shore estuaries because of the naturally low tidal ranges on the north shore.
Anoxic events are mainly caused by human influences over time. Excess nutrients such as phosphorous and nitrogen enter the waterways from groundwater and surface water flow, as well as runoff from agricultural fields, lawns and golf courses, storm drains and sewage systems, and the atmosphere.
There are many long-term measures people can take to contribute to healthier waterways. For instance, homeowners can ensure their septic system is working properly and take care of the fertilizers they put on their lawn, while farmers can practise soil conservation and implement nutrient management plans.
The Department of Environment, Energy and Forestry is currently conducting an annual survey of estuaries across the province. To report an anoxic event, call the department at 368-5044 or toll free 1-866-368-5044.