What is Cryptosporidium a parasite?

Excuse me, could you elaborate on the nature of Cryptosporidium as a parasite? I've heard it mentioned in relation to waterborne illnesses but I'm not entirely clear on its specifics. Is it a bacterium, a virus, or something else entirely? How does it infect its hosts? What are the typical symptoms associated with Cryptosporidium infections? Are there specific preventative measures or treatment options for those infected? Your expertise in this area would be greatly appreciated.