Special regulations and methods pertain to monitoring bacteria in shellfishing waters. Shellfish poisoning is even more frightening than microbial contamination since it can be rapidly fatal, and the toxins are not destroyed by cooking. Let's take a quick look at some key water quality variables you're likely to monitor in estuaries, and see how they differ from their freshwater counterparts. Photo by Tony Williams. It isn't usually monitored in rivers or lakes, unless there is a connection with salt water or concerns about excessive road salting.
Salinity changes with the tides and the amount of fresh water flowing into the estuary.
It is often the major determinant of what lives where. Drinking water is usually less than 0.5 ppt, seawater about 35 ppt. A refractometer measures the change in the direction of light as it goes from air into water. The measurement itself is simple, involving only a drop of water, but the refractometer costs several hundred dollars. Many volunteer monitoring groups use hydrometers to measure salinity.