has water quality datasets for the Everglades National Park, available publicly.
However, the Everglades is one of the most instrumented natural areas of the world. In most of the developing world, water quality data is very spotty as it is much more expensive to obtain water quality data for most parameters ( requiring samping + analysis) as compared to meteorlogical data. Also,water quality can vary wildly spatially as well as temporally, which does not allow meaningful extrapolation of water quality to areas far from sampling points...
The British Geological Survey holds some global data, and might be worth a look. Here's a link to the page that will provide links to the region you're interested in, if they have that resource;
The South African government maintains a water quality monitoring network of numerous water resources (e.g. rivers, dams, estuaries). The landing page is here https://www.dwa.gov.za/iwqs/ . You can follow the link (on the right of the page) to the Water Management System, choose the "Geographical Water Quality Data Exploration Tools" link to go to a page that provides further links (in a table on the left) to site- specific data.