Blue-green algae technically is bacteria found in bodies of stagnant fresh water. This includes lakes, ponds, and even fountains or birdbaths. Blue-green algae thrives in warm, dry weather, and so summer and early fall in Colorado provide the perfect conditions for their growth. Rapid proliferation is known as a blue-green algae “bloom.” Officially known as cyanobacteria, blue-green algae may produce toxins (poison), that are life-threatening to dogs, humans, and wildlife.