Can A Fish Live In My Swimming Pool?
It might sound fun or even relaxing to imagine koi or goldfish swimming alongside you in your backyard pool, but the truth is, swimming pools are not suitable environments for fish. While they’re designed to be safe and enjoyable for people, pools are, quite literally, toxic to fish.
Whether you’re thinking about turning your pool into a pond or just curious about the science behind it, here’s why fish and swimming pools don’t mix.
1. Chlorine and Other Chemicals Are Deadly to Fish
The number one reason fish can't survive in a swimming pool is chlorine. Pool water is treated with a cocktail of chemicals—mainly chlorine or bromine—to kill bacteria, viruses, and algae, keeping the water safe for humans. But to a fish, these chemicals are incredibly harmful.
Chlorine damages gills, making it difficult (or impossible) for fish to breathe.
Even small amounts can burn a fish’s skin and internal organs.
Other pool chemicals, like algaecides, flocculants, and pH balancers, further disrupt the delicate balance fish need to survive.
Fish are highly sensitive to water quality. Even if your pool “looks” clean, chemically treated water is effectively poison to aquatic life.
2. Lack of Oxygenation
Fish need oxygen to survive, and they get it from water—not from breathing air like humans. In a natural pond or aquarium, oxygen is added to the water via circulation, plants, and surface movement. Most swimming pools don’t have the right kind of aeration or biological filtration to support aquatic life.
Even saltwater pools, which use a salt-chlorine generator instead of liquid chlorine, still produce chlorine that’s toxic to fish—and lack the natural ecosystem necessary for fish to thrive.
3. Temperature Fluctuations Can Be Dangerous
Pool water temperatures can swing significantly, especially in hot or cold weather. Fish, especially ornamental species like koi or goldfish, are sensitive to sudden changes in temperature. Pools often heat up during the day and cool rapidly at night—conditions that are stressful and potentially fatal for fish.
4. No Natural Ecosystem
Fish need more than just water. They need:
Beneficial bacteria to break down waste
Plants to provide shade and food
Gravel or substrate for bacteria colonization
A stable food supply and proper pH balance
Swimming pools are sterile, artificial environments. Without these natural features, a fish can’t regulate its biological processes or stay healthy.
5. Poor Waste Management
Fish produce waste, just like any other living creature. In a pond or aquarium, biological filtration systems and natural bacteria break down that waste into less harmful substances. Pools don’t have this kind of filtration. Instead, pool filters are designed to trap debris—not to process organic waste.
Introducing fish would lead to rapid waste accumulation, poor water quality, and eventually disease and death for the fish.
What If You Want Fish in Your Backyard?
If you're drawn to the idea of fish in water, consider a dedicated fish pond or water garden instead. These are specifically designed with the needs of fish in mind, including:
Dechlorinated water
Aeration systems
Biological filters
Plants and shelter
Temperature regulation
You can even convert an old or unused pool into a natural pond, but it requires draining, removing all chemicals, and installing the correct filtration and ecosystem supports.
Final Thoughts
Swimming pools are fantastic for relaxing, exercising, and entertaining—but they are no place for fish. The water chemistry, temperature, lack of oxygen, and absence of a natural ecosystem make them completely unsuitable for aquatic life.
If you’re interested in keeping fish, your best bet is to invest in a proper pond or aquarium setup. It’s better for the fish—and better for your pool, too!
