Crystal Lake is a 31-acre lake located in Middletown, CT. Most of the lake is surrounded by residential housing except for a town beach at the southern end. A private recreational club is located at the northern tip of the lake as is a dam with a gate valve that can lower nearly the entire the lake. In 2008 Crystal Lake was drawn down for most of the winter. The lake is can have very clear water. The shallow southern areas of the lake, which average around 2.0 meters (6 feet) in depth, are more prone to plant growth. There is a state boat launch on the southeast end but only by electric motors are allowed.

Our September 2009 survey found 14 species of aquatic plants, of which minor naiad (Najas minor) and curlyleaf pondweed (Potamogeton crispus) were invasive. These were found mostly in the shallow southern section of the lake. Our survey showed a substantial decrease in curlyleaf pondweed from 2008 due to an experimental early spring herbicide treatment we preformed. Minor naiad; however, was much more abundant than in previous years and was found mainly in the southern and western coves of the lake. Of the native species, coontail (Ceratophyllum demersum) was the most prominent being found mostly in the southern and center  portions of the lake. Other native plants such as snailseed pondweed (Potamogeton bicupulatus), quillwort (Isoetes species), and Robbins' pondweed (Potamogeton robbinsii) were strewn throughout the northern and southern coves as well as around the two islands.