Mother Nature is a messy pool guest.

While disasters such as fires and floods can wreak havoc, even something as minor as a leaf can mar a pool’s appearance.

Fortunately, most organic stains —and even some inorganic ones — can be eradicated with the right chemical and a little scrubbing. Other cases call for more extreme measures, such as performing an acid wash or even scuba diving to scoop the muck out.

Keeping pools clean can be a dirty job.

We’ll look at common and uncommon sources of pollutants and how to restore a pool’s dazzle.

Troublesome trees

Inevitably, there will be a tree or two shedding something in a pool. Some species are more of a nuisance than others.

Cherry blossoms: This tree was a gift from Japan, acknowledging the country’s budding relationship with the U.S. in 1912. But some service professionals would like to give the darn thing back. Cherry blossoms torment technicians in the Virginia/D.C. area where festivals celebrate the species each spring. But they can be found most anywhere.

The cherry blossom, with its distinctive pink flowers, is a pretty source of frustration, blooming typically in March then shedding toward the end of April.

Pools don’t have to be directly under trees to collect volumes of the colorful debris. The tissue-paper-thin petals are carried on the wind. Techs say that skimmer baskets can get so full of them that lids pop off, but the droppings are also small enough to slip through the mesh and clog up the filter.

“It’s like confetti,” says Myles McMorrow, owner of Pool Services Network in Arlington, Va. “I probably once spent an hour and a half scooping cherry blossoms off the top after a windstorm.”

Fortunately, there is a technique to make clean-up less of a hassle.

McMorrow recommends using Surface Magic, a product by Jack’s Magic that sweeps debris on the water’s surface. The formula creates a thin layer on top of the water, which pushes floating debris to the side as it spreads. That way you don’t have to make as many passes with the net. Alternatively, you can use phosphate-free dish soap for the same purpose.

Pollen producers: Ragweed, mountain cedar and oak trees constitute some of the biggest sources of pollen. In certain regions, the output from these trees can plague backyards with pesky particles.

“It happens every spring,” says Michael Lacey with Metro Pool Chemical in Fort Worth, Texas. “Everything in the yard will turn green — the barbecue pit, your car and tables.”

One good downpour will wash the pollen away, but the pool retains a hazy, greenish hue.

In addition to pollen, oaks drop spindly seeds called catkins. When these long tassels fall into a pool, they’ll change the water to green or brown and deplete the chlorine.

Another plant that hassles is the eucalyptus, whose flowers leave a rust-like pigment. Additionally, some palm species drop seeds small enough to pass through baskets, but large enough to impede pump impellers. Their long, stringy fibers can jam up the works, too.

As a stain remedy, Lacey recommends granular chlorine shock, which has a higher pH. Just sprinkle it over the affected areas. Some light scrubbing may also be in order. Lacey finds that this approach also helps with other tree debris, such as beads produced by crepe myrtles, which create a brownish stain.

Also, increase the pump run time by one hour for every 10-degree spike in temperature throughout the spring and summer because algae flourishes in warmer water. Finally, advise your customers to keep these trees trimmed back from the pool.

Those darn yard crews

Too often, service technicians are blamed for blemishes caused by careless yard maintenance professionals.

When broadcasting fertilizer, lawn care providers may accidentally toss a little in the pool. Fertilizer is high in iron, so it can create little rust spots on the bottom. Lawn pros also have a tendency to leave clippings in the pool, which can breed algae.

To combat this, apply muriatic acid directly to rust-tinged fertilizer stains. This can be achieved with an acid-dispensing device that attaches to the pole. Simply aim and shoot.

As for the grass trimmings, judicious use of phosphate remover will render them inert.

And you may want to have a word with customers about their groundskeepers’ aim. Don’t confront yard maintenance personnel directly or be too accusatory when speaking with clients, lest you start a turf war.

“We don’t want to stir any pots,” Lacey cautions.

Battling bugs

Certain water-loving pests do occasionally make themselves at home in pools. For commercial properties, this sort of thing can yield nasty reviews on Yelp.

Veteran pool tech Javier Payan recalls having to play the role of exterminator when called upon to remove some of these uninvited guests.

This took place at a resort in the desert community of Anza-Borrego, Calif. , which was plagued by tiny-winged insects seeking refuge in pools across the Coachella Valley. U.S. Fish and Wildlife theorized that the species, called boatmen bugs, were coming from the Salton Sea, where fewer fish were keeping the bug population under control.

Whatever the cause, the phenomenon made for really gross pool parties.

“Imagine you’re in the desert, it’s blazing hot — and there are thousands of bugs in the pool,” says Payan, president of Payan Pool Service in El Cajon, Calif.

The bugs feasted on algae, so Payan administered a healthy dose of phosphate remover, eradicating their food source. Another measure that helped: The skimmers on the resort pool weren’t functioning properly, allowing the pests to congregate on the surface undisturbed. Payan replaced the skimmers, making the water less hospitable.

When waters rise

Sometimes Mother Nature delivers such a wallop that conventional clean-up techniques simply won’t cut it.

When Hurricane Harvey ravaged Houston last year, pools disappeared under water. When they eventually resurfaced, some pros found veritable bowls of muck.

Usually, this would call for a drain and refill, but Harvey complicated matters. Professionals had to be cautious that the exceedingly high groundwater did not pop empty pools out of the ground.

The remedy: Keep the water in while taking the gunk out.

“We had to manually suck out four feet of mud and river sand out of pools,” recalls Kyle Walker, a business development representative for Manning Pool Service.

That meant diving. But there was the issue of water clarity to handle first. Flocculants dropped the suspended particles to the bottom, allowing the divers to see clearly. Using a 4-inch trash pump, they vacuumed up the muck, moving slowly and carefully to not disturb the sediment. Sudden movements would turn the water murky again.

Eventually, after the waters receded, some pools had to be drained due to the organic and inorganic stains from motor oil, dyed woodchips and other storm-swept materials. These pools were not immediately accessible after the storm due to closed roads, and the weight of the storm-swept material left a nasty impression on the plaster. “Typically the chlorine is enough to take care of it,” Walker says, “but when it’s being held down there for a week or more … it can cause deeper issues.”

It took several sessions of acid washing, but the interiors cleaned up.

Likewise, service pros in Florida had massive amounts of muck to deal with after Hurricane Irma devastated the region last year.

Ashes, ashes

The Southern California wildfires that scorched tens of thousands of acres last year left pools looking like murky ashtrays.

In these cases, cleanup consists of a super chlorination treatment of 20 parts per million, followed by a clarifier. Test and treat for phosphates and add algaecide. It may take several filter cleanings before ash and debris are gone entirely.

And yet, that may not be enough.

Payan worries that the water may contain carcinogens. Consider all the toxins that go up in smoke: Roofing tar, tires, plastics, paint and more. Some of that material may be introduced to the water when it comes down as ash.

“We’re out there cleaning all this ash out of pools, but we really don’t know what else is in that,” Payan says.

A drain and refill may be the only way to ensure that the water is absolutely free of anything harmful. Perhaps the homeowner’s insurance would cover the cost.

Says Payan: “As a homeowner, you have the right for the pool to be whole again.”