Cyanobacteria, also known as blue-green algae, are a kind of bacteria found in lakes. These organisms make their own food through photosynthesis. Small animals including mayfly larvae eat the cyanobacteria, and small fish such as yellow perch eat the larvae. The small fish provide food for larger fish, such as walleye. Choose the level of the food pyramid that represents the energy role of cyanobacteria in the lake ecosystem.