North Pond Dam

Will lowering the dam help the water quality in North Pond?

From the Maine DEP (https://www.maine.gov/dep/water/lakes/waterlevel.html):

What is the effect of drawdown on a lake? Is there a beneficial effect on the water quality?

Some lakes are managed to reduce high phosphorus levels with significant (6 feet+) drawdowns, typically in September of each year. For such drawdowns to have a beneficial effect on water quality, the lake has to have:

Very high phosphorus concentrations which peak at a specific time of year, typically late summer,
The ability to drawdown the lake (dam capacity) sufficiently to export a large proportion of the lakes' water and thus much of its phosphorus in a short period of time, and
The ability to rapidly re-fill the lake with relatively low phosphorus water.

Most lakes are not suited to benefit by this technique. Options usually considered by lake associations, towns and others who own dams are for variations of only a few feet at most.

Below are comments from Dr. Danielle Wain, Lake Science Director, 7 Lakes Alliance

What does this mean for North Pond?

While North Pond might meet the criteria for having very high phosphorus levels with a peak at a specific time of year, North Pond does not meet either of the other two criteria described above.

The maximum depth of North Pond is 20 ft and the dam is only capable of being lowered less than 2 feet, which is not sufficient to have a water quality impact. Even if the water level could be lowered significantly, that would cause several significant issues:

A lot of shoreline would be exposed, increasing erosion from waves and wakes and creating more water quality issues.
Dock and mooring infrastructure would be compromised.
Access to Little North from North Pond would be difficult.
The phosphorus and algae would not disappear in North Pond, as we see high phosphorus concentrations and algae > 6 ft down from the surface. Removing the algae at the surface will just give the algae down deeper more access to sunlight so it will grow more.
This would also pass the problem on to Great Meadow Stream and then to Great Pond, causing downstream problems.

The East Pond dam has only about a foot to work with on their dam, so they can’t manipulate it very much
Now we have the threat of spreading more curly leaf pond weed to North Pond

While the filling rate of North Pond is less than a year, most of the rainfall coming into the lake occurs in the spring and our measurements show that runoff does not have relatively low phosphorus, which is the third criteria above. Opening the dam from East Pond to refill North Pond faster is not an option, as East Pond has no inflows and we would just be transferring the issues with low water levels mentioned above to another lake. Additionally, any increased chance of erosion or sediment resuspension will reduce the longevity of the alum treatment on that lake, which was a very large community investment that also would have reduced phosphorus inflows into the Serpentine (and then into North Pond).

While it is tempting to look for a quick fix to the bloom, there are no quick fixes. Manipulating the dam will likely not help North Pond for the reasons discussed above, and may cause problems in other lakes. While we will be investigating all possibilities as we develop the North Pond Watershed Based Management Plan in conjunction with the DEP and other lake management experts, it is never too early to start making sure that runoff from your property is not contributing to the phosphorus in the lake.

Published on 8/24/2021

Updated on 7/18/2022