Personally, I would call them the "shores of the lake". Another possibility is "edge of the lake/water".

Example from literature where both are used: 

On one occasion, while Jesus was standing by the Lake of Gennesaret with the crowd pressing in on Him to hear the word of God, He saw two boats at the edge of the lake. The fishermen had left them and were washing their nets. Jesus got into the boat belonging to Simon and asked him to put out a little from shore. And sitting down, He taught the people from the boat.