You might have seen it in the news: the Lincoln Memorial Reflecting Pool in Washington DC — arguably the most famous pool in the world — turned green within days of a renovation that cost around US$15 million. As someone who gets called out to fix a green pool most weeks on Sydney’s Northern Beaches, I followed the whole saga with professional fascination. Knowing how to fix a green pool is literally my job, and almost everything that went wrong over there is a bigger, more expensive version of what goes wrong in backyard pools right here at home.

One ground rule before we start. I clean pools; I don’t do politics. The story has become a political football in America, with claims and counter-claims about whose fault it all is — and none of that is my department. This article is strictly about the water. The algae doesn’t vote, and neither does the chemistry.

What actually happened to the Reflecting Pool

Here’s the non-political version of events. In the lead-up to America’s 250th birthday celebrations, the Reflecting Pool was drained and renovated at a cost of roughly US$15 million. It was repainted in a darker “American flag blue”, then refilled with water drawn from the Tidal Basin — an arm of the Potomac River that’s naturally rich in nutrients. Within days of reopening, the water had turned green with algae, and reports said the new paint had started peeling as well.

The response escalated quickly: bottles of hydrogen peroxide poured straight into the water, then a US$1.7 million “ozone nanobubbler” installed to try to keep it clear. The latest plan is to drain the whole thing every year for a two-week clean-out.

To put the scale in perspective: that basin holds tens of millions of litres — hundreds of average Sydney backyard pools’ worth of water. But the chemistry that turned it green is exactly the same chemistry I deal with in a 50,000-litre pool in Narrabeen.

Why it went green — the same four ingredients as your pool

Algae needs four things to bloom: warmth, sunlight, nutrients, and no sanitiser. Take any one of them away and it struggles. Give it all four and it will win every time, whether the pool is in Washington DC or Dee Why.

The Reflecting Pool managed to tick every box at once:

• Warmth. Knee-deep water heats up fast in summer — and the new darker paint absorbs more heat than the old lighter surface. I see the same effect here: dark-interior pools run noticeably warmer than light ones, which is lovely for swimmers and equally lovely for algae.
• Sunlight. A vast, shallow, completely unshaded basin. Sunlight reaches every drop of water all day long.
• Nutrients. It was refilled from a nutrient-rich river basin — water loaded with the phosphates and nitrogen that algae feeds on. That’s the same fuel that storm runoff washes into Northern Beaches pools from gardens and lawns, just delivered by the megalitre.
• No sanitiser. An open ornamental basin full of ducks can’t be chlorinated the way a backyard pool can. There was nothing in the water actively killing algae.

Four out of four. If a customer rang me and described those conditions, I’d be telling them their pool was going green before they finished the sentence. No vandals or conspiracies required — warm, sunlit, fertilised, unsanitised water goes green. It’s what water does.

How to fix a green pool — what I’d have done differently

My green pool playbook is the same whether the pool belongs to a family in Seaforth or a national monument. Here’s where I’d have parted ways with the official response.

1. Test before you treat

Pouring hydrogen peroxide into green water is treating the symptom without a diagnosis. In a backyard pool, the equivalent mistake is tipping in bags of chlorine before testing pH and phosphates — chlorine at the wrong pH is mostly wasted, and shocking a pool without dealing with the nutrient load just means it goes green again next week. Fixing a green pool always starts with a water test, not a dose.

2. Deal with the nutrients first

Refilling with nutrient-rich river water is like topping up your pool from a farm dam — you’re importing algae fertiliser by the tonne. Nothing you add afterwards will fully compensate. In a backyard pool the fix is straightforward: keep phosphates low with a phosphate remover, especially after storms wash garden runoff into the water. Starve the algae and every other treatment works better.

3. Keep the water moving

Still, shallow, warm water is a petri dish. Backyard pools stay clear because the water turns over through a filter several times a day. A giant basin with minimal circulation was always going to struggle — and no amount of chemical dosing fixes stagnation.

4. Don’t buy gear to outrun bad fundamentals

A US$1.7 million nanobubbler is impressive kit, but expensive equipment can’t beat free chemistry. I see the domestic version of this all the time: someone buys a top-of-the-line robotic cleaner for a pool with no chlorine in it and can’t work out why it’s still green. Get the water balanced first — then the gear earns its keep.

5. Maintain it — don’t plan to rescue it

The new plan of draining the pool every year for a scrub-out is, to my ear, planning for failure. It’s the crisis-response model: let it go wrong, then stage a big dramatic fix. Boring, regular maintenance beats heroic recovery every single time — it’s cheaper, the water is healthier, and you never end up on the news.

Credit where it’s due: some of the scientists commenting on the saga suggested skipping the chemicals altogether and introducing water fleas and aquatic plants to graze the algae down — essentially turning it into a managed pond. For an unchlorinated ornamental basin, that’s not as silly as it sounds. It’s the one idea in the whole story that works with the water rather than against it.

The honest takeaway for your own pool

Fifteen million dollars of renovation went green in days, because money can’t buy its way past water chemistry. Meanwhile, a modest phosphate treatment and a sensible weekly routine keep thousands of ordinary backyard pools sparkling all summer. That’s the whole lesson: pools don’t stay blue by accident. They stay blue because someone keeps them blue — testing the water, balancing the chemistry, and catching problems while they’re still small.

If your pool has gone green — after a storm, after a holiday, or after a US$15 million repaint — the fix is the same proven process, scaled to your backyard. Craig’s green pool recovery service covers the Northern Beaches and Lower North Shore, and a regular maintenance schedule means you’ll never need it twice. Get a free quote here — no politics, just clear water.