Which type of algae can sometimes cause foul odors or off-flavors in fish?

Blue-green algae, also known as cyanobacteria, are well-documented for their potential to release toxins and produce foul odors or off-flavors in fish. This group of algae can bloom under certain environmental conditions, such as warm temperatures, high nutrient levels, and stagnant water. When they proliferate, they can generate various compounds, including geosmin and 2-methylisoborneol (MIB), which are responsible for earthy or musty tastes and smells that affect both fish and water quality.

In addition to their impact on flavor, some blue-green algae can also be harmful, producing toxins that can negatively affect aquatic life and pose health risks to humans and animals. This is particularly significant in recreational and drinking water sources where the presence of blue-green algae blooms may lead to warning signs or closures for health safety reasons.

The other types of algae listed, such as green, red, and brown algae, typically do not cause the same issues relating to taste and odors in fish and the environment. They often have different ecological roles and do not tend to bloom in the same problematic ways as blue-green algae.