The climate in Groton is considered temperate, with mild summers and cold winters. The town has several waterways, including the Thames River, which flows through it and empties into the Long Island Sound. The water quality in Groton is monitored by the Connecticut Department of Energy and Environmental Protection, and the town has implemented measures to address pollution from stormwater runoff. Outdoor recreation opportunities include fishing, boating, and hiking in the town's many parks and nature preserves. Groton is also home to the Mystic Aquarium and Mystic Seaport, which provide educational and interactive experiences for visitors.
Groton receives approximately 1278mm of rain per year, with humidity levels near 76% and air temperatures averaging around 11°C. Groton has a plant hardyness factor of 6, meaning plants and agriculture in this region thrive during a short period during spring and early summer. Most plants will die off during the colder winter months.