Where can Cryptosporidium cysts typically be found?

Cryptosporidium cysts are commonly found in surface water sources such as rivers, lakes, and streams. This protozoan parasite is typically associated with environments that can be contaminated by fecal matter from animals or humans, which is more prevalent in surface water compared to other sources. Surface waters can accumulate runoff that carries Cryptosporidium from agricultural areas, mining operations, and even urban environments where animals may contribute to fecal contamination.

In contrast, Cryptosporidium is much less likely to be found in treated drinking water because water treatment processes, especially filtration and disinfection methods, are designed to remove or inactivate pathogens including Cryptosporidium. While it may occasionally be detected in groundwater, it tends to be less common due to the natural filtering properties of soil and underground aquifers. Wastewater can contain Cryptosporidium if it has received no treatment or if the treatment is inadequate, but once it is treated to a standard appropriate for reuse or discharge, the presence of viable cysts should be reduced significantly.

Therefore, the presence of Cryptosporidium cysts is most strongly linked to surface water sources where they can thrive and multiply, making that the correct answer.