Why are some protista harmful to living organisms?

Some protista can be harmful to living organisms because they can act as pathogens, causing diseases in plants, animals, and humans. For example, certain protozoa, like Plasmodium, are responsible for malaria, while others can lead to gastrointestinal infections. Additionally, some protists can produce toxins that contaminate water supplies and food, leading to harmful effects on health and ecosystems. Their ability to reproduce rapidly can also contribute to harmful algal blooms, further impacting aquatic life and human activities.