Starve the algae and keep the water moving.

That’s the strategy. Algae blooms need two things to explode in a heatwave: sunlight and nutrients. You can’t control the sun, but you can control what’s feeding the water.

Start with nutrients. That means reducing fertilizer runoff, cleaning up leaves and grass clippings, and cutting back on fish food if you’ve got a pond. During a heatwave, even small amounts of organic matter can fuel a bloom. If you can, add floating plants like water lilies or duckweed — they compete for the same nutrients and block some sunlight.

Next, aeration. Algae love still, warm water. A pump, fountain, or air stone keeps the water moving and breaks up thermal stratification. It also boosts beneficial bacteria that consume the same nutrients algae would otherwise eat. Works best if you start before the heatwave hits.

Barley straw can help some ponds, but it’s slow and not a miracle cure. Chemical algaecides work fast but can kill fish or crash oxygen levels — use them only as a last resort. Prevention is easier than cleanup.

Future You will thank you for the extra ten minutes of aeration and a quick rake of the debris.