Conditions at Halfway Pond

By Leighton A. Price

Halfway Pond, one of Plymouth's Great Ponds, is a large, spring-fed pond surrounded by conservation land, a few homes, and some cranberry bogs. But, despite its size and apparently pristine setting, the health of this pond is fragile.

This past June, Halfway Pond was clear and inviting, but, by the middle of July, elodea pond weed had grown profusely and a major bloom of toxic anabaena algae had turned the water a sickly green.

By early August, heavy masses of pond weed, as much as 3 to 4 feet thick, extended 50 to 100 feet out from the shore around much of the pond. The on-going bloom of algae reduced visibility into the water to just a few inches. The pond smelled like an open sewer for weeks.

Most people stopped coming to Halfway Pond to fish, boat and swim this summer. Pond weed tangled fishing lines, propellers, centerboards, rudders and paddles. Swimmers were disgusted to wade through the thick pond weed where leeches proliferated. People noticed that toxins produced by the algae irritated their eyes, sinuses, and throats.

Although Halfway Pond has an intermittent history of pond weed and algae problems, it was clear to anyone who comes to the pond on a regular basis that the conditions this year were exceptionally bad.

A further observation is that freshwater mussels, which have proliferated in Halfway Pond at least since the 1800s, have all but disappeared in recent years. In addition, casual observation suggests that the turtle population has dropped sharply from last year when, for example, red-belly turtles were abundant.

Over the past year, twenty water samples were taken in locations across Halfway Pond, and these were analyzed by EnviroTech Laboratories. The Total Phosphate (TP) level reached or exceeded a threshold eutrophic level of .03 mg/l in every one of these water samples. The TP levels ranged from slightly higher than the threshold level to nearly 5 times that level. The median was nearly 3 times the threshold level. The causes for such high readings need to be uncovered.

The only other large pond in Plymouth with both a worse pond weed problem and a worse algae problem is Billington Sea. This too is a large, shallow pond with a number of cranberry bogs around it. But, in addition, Billington Sea has many houses, its TP level is substantially higher than the level at Halfway Pond, and funds have repeatedly been spent in attempts to remediate the situation. Can we expect the same fate for Halfway Pond should development occur as has been proposed?  

Halfway Pond is showing signs of serious trouble. Unless we can determine the causes of these problems, take steps to remediate them, and work to keep new stresses on the environment away from its shores, the situation is likely to become much more serious.

The condition of Halfway Pond should serve as a strong warning about the health of water resources in our immediate area and in Plymouth more generally.