Grassy Island Nature Reserve is a small island located about one kilometre east of Tancook Island, near the mouth of Mahone Bay.

The island provides important nesting habitat for terns. Until recently, it supported a colony of endangered roseate tern.

The island is both provincial wildlife management area and nature reserve. The wildlife management area regulations restrict visitation and hunting during the breeding season (March 31 – September 1), as well camping, vehicle use, and habitat alteration year-round.

With nature reserve designation, the restriction on seabird hunting above the mean high-water mark is now year-round.

At less than one hectare in size, Grassy Island is Nova Scotia’s smallest nature reserve.