Euglena are unicellular microorganisms commonly found in nutrient-rich ponds and lakes. Under certain conditions, they can cause water to take on a reddish-brown hue, often mistaken for harmful algal blooms. The severity and frequency of these red blooms are largely influenced by phosphorus levels in the water column. While Euglena play a role in aquatic ecosystems, excessive growth can indicate water quality imbalances. Managing nutrient inputs, particularly phosphorus, is key to preventing these blooms and maintaining a healthy aquatic environment.