Why Do Pools Turn Green? Lessons From the Lincoln Memorial Reflecting Pool

This summer, one of the most recognizable bodies of water in the country turned an unexpected shade of green. Just days after a multimillion-dollar renovation, the Lincoln Memorial Reflecting Pool in Washington, D.C. — freshly resurfaced and painted a deep navy — bloomed with algae, turning its mirror-like surface murky right before a major national celebration. Crews were photographed skimming and vacuuming the water in a race to bring back its color.

‍

If a national landmark with a full restoration budget can go green that fast, it is no surprise that backyard pools do too — especially here in the Sacramento area, where summer heat creates near-perfect conditions for algae. The good news: a green pool is almost always recoverable. Here is why it happens, why it is so stubborn in summer, and how to get your water clear again.

‍

Why Pools Turn Green

‍

Green water is almost always algae — microscopic plant life that blooms fast when conditions line up. A few things usually drive it:

‍

• Heat and sunlight. Algae thrives in warm, sunlit water. The hotter it gets, the faster it multiplies.
• Low or inconsistent sanitizer. When chlorine, or a salt system's output, drops below the right level, there is nothing holding algae back.
• Poor circulation and filtration. Water that is not moving and filtering properly gives algae still corners to take hold.
• Nutrients in the water. Phosphates and nitrogen from dust, runoff, leaves, and even fill water act like fertilizer for algae.

‍

When several of these overlap — a hot week, a busy pool, and a sanitizer level that quietly slipped — a clear pool can turn green in a day or two.

‍

Why Algae Is So Hard to Beat in Summer

‍

The Reflecting Pool situation is a useful illustration of why algae can be so stubborn. Environmental experts noted that midsummer is the worst possible time to fight a bloom, because high temperatures keep pushing new growth. And even after treatment, water often still contains nutrients like nitrogen and phosphorus that feed algae — levels that can be reduced but never completely removed.

‍

That is the catch with green water: killing the algae you can see is only half the battle. If the underlying conditions — heat, nutrients, weak circulation, low sanitizer — are not corrected, the bloom can come right back. It is also why a single bottle of algae killer rarely fixes a truly green pool on its own.

‍

How to Get a Green Pool Blue Again

‍

Recovering a green pool is a process, not a one-step fix. In general, it looks like this:

‍

1. Test the water to see how far off the chemistry is and how severe the bloom has become.
2. Remove debris and brush the walls, floor, and steps to break algae loose from surfaces.
3. Shock the pool with a strong dose of sanitizer to kill the algae.
4. Run the filter continuously and clean it as it loads up, so dead algae is pulled out of the water.
5. Vacuum the settled debris once the algae dies and drops.
6. Rebalance the chemistry so the water is safe, comfortable, and stable again.

‍

For mild cases, this can clear up in a few days. For a deep green or long-neglected pool, it takes longer — and the most severe cases sometimes need to be drained and refilled, which is exactly what experts suggested might be required for the Reflecting Pool.

‍

Keeping It From Coming Back

‍

The best defense against a green pool is consistency: steady sanitizer, regular brushing and skimming, clean filters, and water chemistry that is checked and adjusted before it drifts. In Sacramento's long, hot summers, that usually means staying on top of the pool weekly rather than letting it coast between cleanings.

‍

When to Call a Pro

‍

A light tint can often be handled with careful at-home treatment. A fully green, cloudy "swamp" pool is another story — it takes the right testing, the right sequence of treatment, and enough filtration time to clear safely.

‍

That is where we come in. At Nevergreen Pools, our Green Pool Clean-Up and Algae Removal services are built for exactly this — clearing the water and correcting the conditions that caused it, so your pool does not just look better today but stays that way. If your pool has gone green this summer, reach out and we will help you get it back to blue.