Fairlands Valley Lakes comprise the largest area of open water in North Hertfordshire. Constructed in 1972 the lakes consist of, the Main Lake (the Sailing Lake) at the Six Hills Way end, the Millennium Lake with an island, the Environment Lake, and the Balancing Pond at the Fairlands Farm End. As Fairlands Valley has no stream or natural spring, the Lakes rely on surface water draining into the Valley from the eastern end of Pin Green. Two large storm drains were built to channel water from the Chells Way end of the Valley into the Balancing Pond, and from there into the three lakes. At times of high water levels the Lakes drain into Fairlands Valley on the western side of Six Hills Way.

The Lakes have provided breeding habitat for several species of wildfowl and a resting and feeding site for birds on passage and migration. It is from the Lakes that some of the more unusual species have been recorded. Unfortunately in recent years such records have become scarcer, possibly due to the maturing of the site, and by the increased use as the recreational facility for which of course it is intended. Improvement works have been made to all three lakes, the Environment Lake (2001), the Millennium Lake (2000), and the Main Lake (2008), when each was drained. Early morning visits are recommended.