Winter, spring, summer — the three markedly define the seasons. A simple association produces thoughts of new buds on trees, chilly temperatures or the wilting heat of a hot and humid day.

This year, however, the three seasons have something in common: plenty of rain. It’s that plenty of rain that has directly and indirectly led to advice by the experts to be a little more cautious about swimming in the local waterways.

There are two separate things happening in the river. The first, is that so much rain leads to much fresher water than can usually be found midsummer in Beaufort County (notice the lack of jellyfish). Certain types of algae thrive in fresh water — an example would be filamentous bluegreen algae, which has caused the green water people have seen in Bath over the past little while. This algae can be toxic under certain circumstances, but there’s been no indication it’s toxic here.

The amount of rain also can be responsible for the presence of bacteria, called enterococci, in the water. The question is: what is it? This type of bacteria is found in the intestines of warm-blooded animals, which is quite a range of animals — the top end of that range would be human.

According to the Environmental Protection Agency, there are several common sources of enterococci in the water.

First on the list is pollution from wastewater treatment plants and sewage systems — bacteria from sewage can enter the water because of system failures, perhaps leaky pipes and storm overflows.

Since much of Beaufort County is farmland, it makes sense that runoff from agricultural land also can be a primary source of enterococci. Manure from livestock or poorly stored slurry (liquid manure from large livestock rearing companies) can wash into water bodies.

Water draining from urban areas by street drains can include animal and bird feces from roads and other paved surfaces.

Domestic sewage also can end up in the water through misconnected drains or poorly located or maintained septic tanks

The fact that there’s enterococci in the water does not mean that someone will get ill when swimming, but its presence is closely tied to other bacteria that will make one ill. That’s why “No Swimming” signs went up in a few places a couple of weeks ago. They promptly came down again when the samples showed the levels were within accepted EPA and state standards.

With the algae, people should simply be paying attention: if it looks weird and smells weird, don’t swim. With enterococci, people should also be paying attention: if the signs are up or there’s been a heavy rain, don’t swim.

Take common sense to the river.