The lakes are modelled using a two layer code. The first layer has a minimum depth of 1m, while the second layer is unlimited. Lake mass is effected by precipitation, evporation and lake ice melt and freeze. In addition, river inflow from upstream boxes and outflow to the downstream box modify the first layer properties. There is a small amount of heat diffusion at the interface, and convective overturning occurs if the temperature stratification is unstable.