Algae blooms can appear as large, discolored patches on the surface of water bodies, often with a green, blue-green, or reddish tint. These blooms can give the water a thick, soupy appearance and sometimes emit foul odors. They are caused by the rapid growth of algae, often due to excess nutrients like phosphorus and nitrogen in the water. Algae blooms can be harmful to aquatic ecosystems and even pose risks to human health if they produce toxins.