Why is the drawdown level different year to year?
So if that’s all true, why does the depth change every year? The drawdown is a really effective tool for
managing aquatic plants because it exposes them all to the freezing air no matter what – but that means
it also exposes everything else that lives in those shallow parts of the lake to freezing air too! Native
plants, shellfish, and other critters that use that area for habitat and hunting all risk being killed by the
drawdown the same way the drawdown kills Eurasian watermilfoil. To try to mitigate the impact on those helpful
parts of the ecosystem, historically it’s been helpful to only do a deep drawdown every other year
– giving those organisms a fighting chance to keep their population intact. The area of the lake that is
exposed in both shallow and deep years is routinely devoid of almost all plants since the drawdown is such an
impactful tool. However, if there was a deep drawdown every year, there would be substantially fewer plants in
the lake – preventing fun sportfish (like our famous smallmouth bass) from having a place to reproduce
and their young to survive being hunted. One other aspect to consider is that deeper drawdowns increase the
rate of shoreline erosion in the lake. By exposing more lakebed to the air, you destabilize the sediment, and
when the lake refills in the spring that destabilized sediment will fall off the shoreline and enter the water.
This can contribute nutrients to the water that fuel algae growth, and harm the structure of the lake’s
shore. By switching the drawdown depths every year, the rate of this increased erosion can be slowed
Why is this so complicated?
It can be easy to forget just how complicated of an ecosystem a lake is; each part interacting with each other
in a complex “dance”. So as lake managers it’s hugely important that we try to maintain a
healthy balance of each of those parts whenever we think about impacting that ecosystem. The Candlewood Lake
Authority (CLA) does not control the drawdown – FirstLight, with some requirements set on them by FERC
(the federal agency responsible for overseeing hydropower projects), controls the depth, timing, and extent of
the drawdown every year. However, we sit on a committee with the State of CT DEEP, federal agencies, and the
lakes Zoar and Lillinonah Authorities (remember, the water from Candlewood eventually reaches Lillinonah and
Zoar) to discuss the plan for the drawdown each year and advocate for what we feel is best for our lake based
on the science and monitoring we do. One side benefit of the drawdown, and a common topic of discussion this
year (2021), is that the drawdown is also very effective at killing adult zebra mussels exposed to the air in
addition to the plants.