Australia’s wildfires have already had catastrophic effects on animal and plant life on land, killing an estimated one billion animals. But did you know that wildfires also affect nearby waterbodies?

The consequences wildfires have on oceans are less obvious, but they can be devastating.

Wildfire smoke and debris may be transported into the ocean by wind or rain. Plumes of ash and smoke can be picked up by the wind and blown to the sea, or storm runoff can carry charred matter from the ground into the ocean as it flows across the burnt land.

The Santa Ana winds carry smoke towards the Pacific Ocean during Southern California wildfires in 2017. Photo by NASA Goddard Space Flight Center

When wildfires travel through an area, they consume everything in their path. In their wake, they leave behind huge amounts of scorched plants and ash. Wildfires also cause the ground to become “hydrophobic,” meaning it repels water (so water can’t be absorbed).

When heavy rains fall, the water will not be able to penetrate the soil. Instead, the water will flow over the land and into nearby waterbodies, carrying with it the silt and ash.

Photo by fvanrenterghem

How do wildfires affect our water?

1. Smoke and ash choke ocean life

Once in the ocean, the charred matter from wildfires smothers marine plants and animals. The burnt debris blocks the gills of fish, making them unable to breathe. The matter also prevents sunlight from reaching seagrass and seaweed.

Wildfires can suffocate coral reefs, which happened in the Indian Ocean after the 1997 Indonesian forest fires. Plant life isn’t able to photosynthesize the sun’s light if it doesn’t reach them, and this can have consequences for entire ecosystems.

Seagrass and seaweed provide important habitats and food for many species. Their degradation sends shockwaves throughout entire ecosystems, affecting the entire food chain, not only the creatures that directly rely on these plants for survival.

Photo by Henry Burrows

2. Phosphorus, nitrogen, and potassium can cause algae blooms

Along with charred matter, things like phosphorus, nitrogen, and potassium can end up in the water. Excess nutrients entering the water sometimes causes algae blooms.

When an overload of these nutrients enter the water, they can cause harmful algal blooms like blue-green algae or red tide. Algae blooms may be toxic to humans and pets. They also remove oxygen from the water and limit light penetration, suffocating marine species.

Photo by European Space Agency

3. Metals and chemicals can enter waterbodies

In addition to nutrients, metals can be released when plants and other natural matter combust. Metals like iron and manganese from the wildfire ash can enter watersheds when heavy rains happen after wildfires, as was the case in Canberra in 2003.

Various chemicals in runoff from burning houses and cars may also find their way into waterbodies after a wildfire, degrading water quality and making it unsafe to swim.

How can you swim safely when there are wildfires nearby?

It’s always a good idea to check the water quality before you head to your favourite beach, but it’s especially important to check it if there are wildfires in your area.

Smoke over Venice Beach in 2016. Photo by JD Lasica

As our climate changes, wildfires are happening more and more frequently. They’re getting larger and hotter. They’re becoming even more disastrous and consuming bigger areas of land.

The effects of wildfires are quite apparent on land, but what happens on land will always have consequences for our waters.

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