When swimming in open water, one should always take water movements, shipping traffic and abrupt changes in deep/shallow water into account. By swimming in places where supervision is present, one can enhance his/her safety.
The bacteriological status of open water is an important factor, to determine whether the water can be qualified as swimming water. The bacteriological quality can tell a lot about the presence of the germ of a disease. During a warm summer the quality of water can stagnate. If the water reaches 20 °C or more, it can create a breeding ground for botulism
. Another problem for water quality are floating alga layers. Some of these layers can contain blue algae
, that are poisonous for humans.
Places where rats come, form an increased risk for the illnes of Weil
. It is for this reason, why throwing waste on the beach or in the water is forbidden. If someone gets (severe) health complaints after swimming in surface water, he/she should go to the doctor or GGD