The bugs swimming around in your pool are almost certainly water boatmen or backswimmers, two aquatic insects drawn to pools that have algae or other tiny food sources. Neither carries disease, but backswimmers can deliver a painful sting-like bite if you bump into one. Getting rid of them requires removing their food supply first, then making the water inhospitable.
Water Boatmen vs. Backswimmers
These two insects look similar at a glance, but they behave very differently in your pool. Knowing which one you have helps you understand the problem and target your cleanup.
Water boatmen are small, flat, brownish bugs with fine black lines across their backs. They cruise along the bottom and feed on algae and microscopic organisms, scooping food with spoon-shaped front legs. They cannot bite people. Water boatmen are strongly attracted to lights at night, so if you leave your pool lights on after dark, you can draw swarms of them. They fly well and will land on any lit water surface they can find.
Backswimmers are larger, swim upside down near the surface, and have a distinctly triangular, keel-shaped body that lets them move quickly through the water. They’re usually marked with bold patches of black, yellowish-brown, red, or white. Unlike water boatmen, backswimmers are predators. They hunt mosquito larvae and other small insects, including water boatmen. They have a beak they use to bite prey, and if you handle one or accidentally press against it, the bite feels like a bee sting. It’s painful but not dangerous.
Here’s the typical progression: algae grows in slightly neglected water, water boatmen arrive to eat the algae, and then backswimmers show up to eat the water boatmen. Eliminating the algae breaks the entire chain.
Why They Chose Your Pool
Water bugs don’t randomly appear. They arrive because something in your pool is feeding them or making conditions comfortable. The most common trigger is algae, even the kind you can’t easily see. A thin film of algae on the walls or floor of your pool is a buffet for water boatmen. Once they establish themselves, backswimmers follow.
Low chlorine levels let algae take hold. If your pool chemistry has drifted, with chlorine too low or pH out of range, microscopic algae can bloom quickly in warm weather. Poor circulation from a clogged skimmer basket or an underperforming pump compounds the problem by creating stagnant zones where algae thrives.
Outdoor lighting plays a big role too. Water boatmen fly at night and navigate toward light. A bright pool light, porch light, or landscape lighting near the water surface acts as a beacon. Backswimmers, on the other hand, are mostly active during the day and rarely attracted to lights.
How to Get Rid of Them
Shocking the pool alone won’t solve the problem. Many pool owners dump in heavy doses of chlorine expecting the bugs to die, but chlorine and shock treatments are not effective at directly killing water boatmen or backswimmers. These insects breathe air, not water, so water chemistry doesn’t suffocate them the way it would kill bacteria or algae.
The real strategy is a three-step process: remove the food, break their breathing mechanism, and keep them from coming back.
Step 1: Eliminate the Algae
Balance your water chemistry first. Check pH, alkalinity, and chlorine levels, and make adjustments. Then scrub the walls and floor of the pool thoroughly to loosen any algae film. After scrubbing, shock the pool to oxidize the algae you’ve dislodged. Follow up with a quality algaecide to prevent regrowth. Some pool owners have reported good results with BioGuard Back-Up algaecide, noting bugs dying off within 24 hours of treatment, likely because the product eliminates the food source so effectively.
Check your chlorine and pH levels every two days during this process to make sure the water stays balanced.
Step 2: Use Dish Soap to Drown Them
This is the trick that actually kills the bugs directly. Both water boatmen and backswimmers trap tiny air bubbles against their bodies using water’s natural surface tension. They carry these bubbles underwater to breathe. Dish soap is a surfactant that breaks surface tension, which means the bugs can no longer collect air. They run out of oxygen and drown.
For a standard 20,000-gallon pool, about a quarter cup of liquid dish soap spread across the surface is a reasonable starting point. Dawn Ultra is a commonly recommended brand. The soap is so diluted at that ratio that it won’t create a bubble problem in the pool. If the first application doesn’t clear them out, add a bit more. Reapply weekly or biweekly as needed until the population is gone.
Step 3: Skim and Clean
While the soap and chemistry do their work, manually skim dead and living bugs off the surface daily. Clear out your skimmer baskets so they can catch bugs passively. Run your pump to keep water circulating, since stagnant water is where problems concentrate.
Keeping Them Out Long-Term
Prevention is entirely about making your pool uninteresting to these insects. Consistent water chemistry is the foundation. If algae never gets a foothold, water boatmen have no reason to visit, and backswimmers have no prey to hunt.
Lighting changes make a surprisingly big difference. Switch to warm-temperature LED bulbs around the pool area. Insects respond far less to warm light than to cool white or blue tones. Angle your lights to shine across the deck rather than directly over the water, and put them on a timer so they shut off earlier in the evening. Many pool owners notice a drop in bugs within the first week of making this switch.
A pool cover during peak bug season blocks insects from landing on the water to begin with. Just be careful that the cover itself doesn’t become a breeding ground. Rain collects in low spots on a cover, and a mosquito needs only about a bottle cap’s worth of still water and five days to lay eggs. Pull your cover taut or drain any standing water after rain.
Landscaping around the pool matters too. Dense vegetation right up to the pool deck gives insects a convenient highway from garden to water. A two-foot border of gravel or bare ground between planting beds and the pool deck disrupts that path and also helps reduce ants. Trim back any branches or shrubs that overhang the water. Keep the deck dry overnight, since wet surfaces attract insects looking for moisture.
Run your pump daily, even when you’re not swimming. Moving water discourages egg-laying and keeps chemistry more consistent. Walk your yard after rainstorms and tip over anything holding standing water: flower pot saucers, toys, buckets, folded tarps. Every small puddle is a potential mosquito nursery, and mosquito larvae are exactly what draw backswimmers to your property in the first place.