I'm sure others have discovered this, but for those who haven't ... you are normally not allowed to build a Dock to increase the food production on freshwater lakes, they give you 3 fish/square as it is which is decent especially with an Expert Fisherman's bonus.
However, if you find a freshwater lake that is only one square away from a sea square, if you build a settlement so that it touches both the sea square and the freshwater lake, you get the Dock food production bonus on the freshwater lake as well as the sea squares, which can really give you a lot of food in some setups (especially if your settlement borders more than one freshwater square!).
This is a bit of an exploit, since the game doesn't allow you to build a dock to get extra advantage of freshwater lakes, but like the Silver Market crash and boom economic war, I find I tend to do it anyway to help me get every last dirty trick advantage I can.
However, if you find a freshwater lake that is only one square away from a sea square, if you build a settlement so that it touches both the sea square and the freshwater lake, you get the Dock food production bonus on the freshwater lake as well as the sea squares, which can really give you a lot of food in some setups (especially if your settlement borders more than one freshwater square!).
This is a bit of an exploit, since the game doesn't allow you to build a dock to get extra advantage of freshwater lakes, but like the Silver Market crash and boom economic war, I find I tend to do it anyway to help me get every last dirty trick advantage I can.