The phrase "small lake" refers to a small body of water. It describes a body of water that is smaller in size compared to larger lakes. Full definition
Small lakes with a surface area of less than 100 m2 represent the majority of global freshwater ecosystems. (sciencedaily.com)
We have a few small lakes starting on the grounds here at the park. (okcpetsmagazine.com)
But that's a reflection of the extent to which the entire watch and wearables markets are small lakes relative to the vast ocean of the smartphone market. (vox.com)