What inference can you make about the effect of tides on health in jamestown

Jamestown was located on a site that was too remote for agriculture - in fact, the whole island was isolated because it was swamp-like, infested with mosquitos and and the only water came from tidal rivers. This water was not safe to drink, which could have led to a number of waterborne diseases causing health problems, such as cholera, typhoid or dysentery.