When is it safe to swim in the ocean or river after heavy rain?

It may be an El Niño summer, but that hasn’t stopped it from raining over much of Australia.

In the run-up to December, much of the country experienced wetter conditions than normal for that time of year. The weather has also been temperamental, with thunderstorms one day followed by perfect beach weather the next.

These backflips from storm to sunshine create the perfect conditions for a little-known danger: water pollution caused by heavy rain.

“It’s easy to think about breakers, waves, sharks and blowflies, but water quality is probably at the bottom of the list,” says Associate Professor Ian Wright, a water scientist at Western Sydney University, “and that could be the problem.” most important in terms of human health.

No Australian summer would be complete without a trip to the beach, river or water hole, so how do you know when it’s safe to get back in the water after a fall?

The general rule for swimming after the rain.

After heavy rain, it is generally recommended to avoid swimming in the ocean for a day or two. Wright, who is an avid swimmer, says it’s safest to wait at least two days before returning. For estuaries, the NSW Office of Environment and Heritage recommends waiting up to three days.

After a major flood, overflowing stormwater and sewage flows into the ocean, rivers, and lakes, contaminating the water with bacteria, viruses, and chemicals. While there is no standard for what is a dangerous amount of rain, Wright says more than 10 or 20 milliliters “is quite a lot.”

In busy urban areas, all kinds of nasty substances end up in storm drains, including oil from vehicles, debris from workplaces, grease from restaurants, bacteria-laden dirt, yard waste, and dirt. garbage in general. In rural regions, pollution from agriculture and industry are the main risks.

A stormwater drainage outlet at Bondi Beach, Sydney.(ABC Radio Sydney: Luke Wong)

“If it’s left on roads, the rain will wash it through storm drains and into catchments,” says Corrine Cheeseman, chief executive of the Australian Water Association.

“There is a dilution effect, the ocean is very large, but particularly in those first few days there is a surge of whatever has been on the surface reaching the oceans.”

However, the main risk to swimmers is feces, whether it’s pet waste dumped into drains, farm animal waste, or overflowing human sewage systems (we’ll look at why this is particularly dangerous in the next section).

The sewer and stormwater systems are connected, and when the sewer side becomes blocked or overflows, it is redirected to the stormwater line. This means that excess waste bypasses the treatment plant and is discharged directly into the ocean. This is a bigger problem in urban centers, where populations have grown beyond what the system can easily handle.

“Often the sewer pipes are almost full and when it rains, a large percentage of the runoff enters the sewers,” Wright says. “Our sewage systems can’t handle a wet climate anywhere like they can in a dry climate.”

It’s disgusting, but why is it dangerous?

While the thought of diving into the ocean and taking a drink of water laced with human waste is unpleasant, to say the least, it is also a danger to our health.

The most common medical problems, says Wright, are ear, nose and throat infections and digestive disorders caused by bacteria and viruses in feces.

To determine if fecal matter is present, water analyzers look for the presence of enterococci, an organism commonly found in the waste of warm-blooded animals.

These water samples are typically collected once a week, but enterococci results take two to three days after sample collection to be confirmed.

In New South Wales, you can find the water quality on the government website. beach watch website, which allows you to search by swimming spot (or check its status below).

Consider the location

When choosing where to swim after a heavy rain, there are two things to consider: what is in the environment that could contribute to pollution and how often the water is recycled.

For example, swimming spots in harbors are riskier than coastal beaches due to their proximity to industrial areas and the fact that water circulates more slowly, meaning pollutants take longer to dilute. The same can apply to small streams, which flow slowly, or lakes that have little or no movement.

In contrast, beaches exposed to strong tides, especially those isolated from urban centers, are likely to empty more quickly.

“It’s really hard to say it’s the same everywhere because it depends on the uses of the watershed, but also how the water flows and dilutes everything that washes away,” Cheeseman says.

To swim or not to swim

In the event of heavy rain, some beaches may be closed to bathers.

But if a location remains open, people should consider the amount of rain, how much time has passed between showers (if it hasn’t rained for a while, pollutants will have had more time to build up), and the characteristics of the location before making the decision. . your decision. Surf Life Saving clubs and local councils can also put up signs warning of pollution.

Where to find information about water quality

New south Wales: beach watch Includes information on beaches throughout the state.
VIC: EPA Victoria publishes data on beaches in Port Phillip Bay and swimming spots along the Yarra River
ACT: He territorial government monitors the condition of lakes, ponds and rivers
Queensland: Please check specific council sites for up to date information.
South Australia: EPA Pvt. publishes warnings about beach water quality
NEW TESTAMENT: He NT Water Data Portal publishes information about the territory’s water sources
WASHINGTON: The states Health Department assigns quality ratings for beaches, rivers, streams and lakes
TAS: A map of water monitoring sites can be obtained. found here

But the most important thing, Wright says, is that you should trust your instincts: If something seems wrong, it’s probably best to err on the side of caution. “You can actually smell it and see the discoloration,” she says. “We can’t see individual bacteria, but the cloudier and dirtier the water is, the riskier it is.”

If you’re still unsure, Cheeseman suggests checking your local council or water monitoring website for information. “We have a pretty good system in Australia and generally these sorts of things are monitored and measured,” she says. “And certainly, if there was something that could have a serious health impact, you would expect there to be some kind of warning about swimming at certain times.”

If you swim in isolated or remote areas, especially inland rivers or waterholes, it may be more difficult to find information. In that case, you will have to rely on local knowledge and your own judgment.

“When you go to the Australian outback, good luck finding information about where you can swim,” says Wright. “And since there’s no official advice, it’s really important to make very careful decisions.”

And finally, how about swimming while it rains?

“It totally depends on the amount of runoff,” Wright says.

“When it starts to rain, it is absorbed before the water accumulates and runs down the sewers, streets and drains.

“If it rains lightly and doesn’t create runoff, it’s probably fine. In fact, it’s probably one of the loveliest times to swim.”