Lakes do not always stay the same. Streams may empty into lakes. The lake may lose its water and dry up. Lakes, ponds, rivers and streams are fresh water. Rivers empty into the largest body of water, oceans.
Oceans contain salt water.
Fill the bowl with water. Have the students write a story about how the pond was formed. Lakes - Press a bigger bowl into a box of loose soil or sand. Fill the bowl with water. Have the students write a story about how the lake was formed.