SUMMER FISH KILLS

With summer weather warming up lakes and ponds, fish kills may be discovered in area waterbodies. The sight of dead and dying fish along the shores of a favorite pond can be distressing and trigger concerns about pollution. Fish do act as the "canary in the coalmine", so it's natural to think a fish kill was the result of pollution. In fact, the opposite is likely true; the vast majority of fish kills reported are natural events.

Natural fish kills are generally the result of low oxygen levels, fish diseases or spawning stress. Dissolved oxygen depletion is one of the most common causes of natural fish kills. As pond temperature increases, water holds less oxygen. During hot summer weather, oxygen levels in shallow, weedy ponds can further decline as plants consume oxygen at night. This results in low early morning oxygen levels that can become critical if oxygen levels fall below the requirement of fish survival. In addition to reduced oxygen levels, late spring and early summer is when most warmwater fish species, such as sunfish (bluegill, pumpkinseed, largemouth bass) begin to spawn. At this time, large numbers of these species crowd into the shallow waters along the shore vying for the best spawning sites. These densely crowded areas become susceptible to disease outbreaks, especially as water temperatures increase. The result is an unavoidable, natural fish kill.

When a caller reports a fish kill, a MassWildlife fisheries biologist determines whether the kill is natural or requires a site investigation. If the incident is determined to be a pollution kill, MassWildlife notifies the Department of Environmental Protection for analysis of water and fish samples as well as a formal investigation.

To report a fish kill, contact Richard Hartley at 508/792-7270 x132, Monday through Friday between 8:00 am and 4:30 pm, or one of the five MassWildlife District Offices: Pittsfield 413/447-9789;  Belchertown 413/323-7632; W. Boylston 508/835-3607;  Acton 978/263-4347;  Bourne 508/759-3406.   After normal business hours or on holidays and weekends, contact the Environmental Police Radio Room at 1-800-632-8075.