Why is Wenham Lake so low even after such a rainy summer? 

If you’ve been driving down 1A recently between Beverly and Wenham, you probably noticed that Wenham Lake is noticeably low right now. But… It has been raining all summer! How can that be?

Why is Wenham Lake so low even after such a rainy summer? 

The Wenham Lake we see now as we drive down 1A is not the same as the Wenham Lake that you might read about in local history accounts when the Lake was a fishing ground and an ice-harvesting location. If you’ve been driving down 1A recently between Beverly and Wenham, you probably noticed that Wenham Lake is noticeably low right now. But… It has been raining all summer! How can that be?

Today, the lake and the land around it are owned and managed by the Salem Beverly Water Supply Board (SBWSB), which operates the lake as a drinking water reservoir to provide water supplies to the cities of Beverly and Salem. The decision to use Wenham Lake as a drinking water reservoir stems from a legislative act from 1865. Currently, SBWSB refills its two largest reservoirs (Wenham Lake and Putnamville Reservoir in Danvers) with water from the Ipswich River in the winter months when river levels are highest. It then uses water from Wenham Lake in the summer to supply Beverly and Salem with drinking water. That means that Wenham Lake levels will be highest in May, when the refilling season closes, and will drop continually through the summer and into October, when it typically reaches its lowest level of the year. 

But what about precipitation levels? Doesn’t that impact the level of Wenham Lake?

Not significantly!  The reservoir does not naturally refill in any significant way from rainfall because its watershed is quite small and does not keep pace with the rate of water removed in the summer for drinking water supplies. Under “natural” conditions, the water flowing into Wenham Lake would come from groundwater and nearby streams from the area towards Beverly Airport and around Norwood and Beaver Ponds and Longham Reservoir. The capacity of the lake was increased in the late 1800s with the addition of a small dam, which raised the height of the lake by about 10 feet. So the lake under “natural” conditions would be quite a bit smaller than it currently is and groundwater levels alone would not fill the lake at its current size. 

I thought the lake levels were lowered for vegetation management?

We too have heard this theory that Wenham Lake levels are lowered to manage vegetative growth around the edges of the pond. This is a very well-informed theory because some lakes are drawn down in the winter specifically to manage vegetative growth. However, Wenham Lake does not use this “winter drawdown” technique. The water levels released from the Lake are in direct response to water demand from the cities of Salem and Beverly. Some vegetation management around the edges of the lake is done when water levels are low, but it is not the primary driver for dropping water levels.

Are you looking for more information on Wenham Lake?

Check out these resources from a Brown Bag Lunch session at The Wenham Museum:

Watch the presentation on YouTube

View the PowerPoint from Erin Bonney Casey, IRWA

View the PowerPoint from Ernest Ashley, Town of Wenham