In, On & At

Five meanings for IN, ON and AT: 1) There are thousands of fish IN the lake (= completely inside) 2) There are several islands IN the lake (= surrounded by it) 3)     There are some sailing boats ON the lake (= on the surface of the water) 4) There's a small town ON the lake (= on the line made by the lake shore) 5) There are crowds of people AT the lake today ( = at the point on the map where the lake is)