Cryptosporidium parvum is a microscopic parasite that causes gastrointestinal illness known as cryptosporidiosis. It is commonly found in contaminated water, particularly in swimming pools, lakes, and drinking water. The parasite can survive in harsh environments and is resistant to many disinfectants, making it a significant public health concern. Infection with Cryptosporidium parvum can lead to symptoms such as diarrhea, stomach cramps, and nausea. While healthy individuals may recover without treatment, those with weakened immune systems, such as people with HIV/AIDS or undergoing chemotherapy, are at higher risk for severe illness. Proper hygiene and water treatment are essential for prevention.