Complex sentence: Etherow Country Park has many local groups associated with it; the "Friends of Etherow" are a small local community group; other groups include Anglers, the afore-mentioned sailing club, and model boaters.
Split into simpler sentences: Etherow Country Park has many local groups associated with it. The friends of Etherow are a small local community group; other groups include the anglers, the sailing club and the model boaters.