Arizona's Unique Desert Pool and Its Mysteries

Not a single fish can breathe in the water of a desert pool in Arizona's Verde Valley. 386 feet across, the pool constantly pushes out about a million and a half gallons of water— and it never runs dry. The water is toxic to fish, which is why it's a unique oasis for five rare species found nowhere else, including a leech that doesn't drink blood.

Neither a Pool, Nor Fishable

Deep within a limestone sinkhole in a valley, a pool was born. The Verde Valley in Arizona is home to this unique sinkhole, which has never ceased to flow. The desert pool is 386 feet across, and each day, it pumps out around 1.5 million gallons of water. This pool is perpetually filled, with water fluctuating less than six inches throughout the year and maintaining a steady temperature of 70 degrees. The pool's most distinctive feature is its toxicity to fish. The water, which flows through vents from the bottom, is saturated with high levels of carbon dioxide. The abundance of carbon dioxide is more than a hundred times what ordinary water carries, poisoning any fish that tries to take a breath. A mineral-rich desert pool, in essence, it is nothing like other natural bodies of water.

The Ecosystem of Exceptionality

Arizona's Verde Valley is no stranger to peculiarities. The desert landscape surrounding the pool is punctuated by the occasional oasis, providing life to plants and animals once thought impossible. The limestone sinkhole shares this characteristic. The pool's unique feature — its toxicity to fish — has made it a habitat for rare breeds, some of which exist only in this pool. Nature has discovered a way to make use of this poisoned pool as a home to life found nowhere else on Earth. The pool's high concentration of carbon dioxide makes it an excellent habitat for an endangered leech, which cannot consume blood but instead hunts by sensing vibrations in the water. At an hour after sunset, the leeches rise from the bottom to feed. By morning, their empty shells are floating on the surface. Profit from the leech's unique feeding habits has been long recognized by the Sinagua people. A thousand years ago, the Sinagua built their homes atop the sinkhole, crafting irrigation ditches to harness the pool's water for daily usage — which remain in use today.

Hunting in the Dark

The pool’s atmosphere of death is not a deterrent to leeches, but it is an advantage. To us, leeches might seem like ghastly creatures, but to the pool, they are a testament to life in the face of adversity. Every aspect of the pool’s characteristics only serves to make it exceptional. The desert pool's flowing nature, along with its temperature range and chemical composition, make it a haven for life. The leeches themselves are unique. Instead of suckling blood from hosts, they have an unusual method. It is not on land or in the pool's floor they find their prey. They rise from the floor of the water to eat, waiting for vibrations of water movements to guide them to their food. Occurred by the hungry leech's vibration sensing, the prey is then swallowed whole. A unique feature of humans would be a higher level of our curiosity to know how these lethal-looking creatures survive. If the pool is a mystery, then these leeches are a mystery hidden within it.

The Simplified Feed Cycle

The creatures that call this pool home have adapted a unique strategy for survival. Unlike their land-dwelling counterparts, the aquatic leeches in this pool feed in unusual ways. They don't absorb parts of their prey. Instead, they wait in the water for prey to pass by. No other leech on the planet is known to do that. The leeches take advantage of the low temperatures and chemical composition of this desert pool. By sensing vibrations in the water, they can detect their prey and swallow it whole. This diet of dead, partially decomposed organisms makes them a crucial part of the ecosystem. Breakdowns of dead and decaying matter are an essential task in the life cycle.

Human impacts on the pool

The pool not only sustains itself, but it also provides life to people. The Sinagua people carved homes into the rim and also dug irrigation ditches to tap the well. The pool's water was essential for their daily living. They not only made use of the water from the pool but also excavated it for other uses that are still visible today. Irrigation ditches constructed in the pool are still in use today. The pool's water is still used for gardening and more. The pool's waters have nourished and continue to nourish thousands of lives.

For Those Who Dare

Travel to Arizona's Verde Valley to see the sinkhole pool for yourself. But if diving is your objective, take care. The pool's swimming environment is not the only thing you should take into consideration. The pool's water has a different chemical composition, which can be poisonous for anyone in prolonged exposure to it. Before you decide to swim in the pool, bear in mind:

• Get Clearance: Since the area is controlled by the Sinagua people, permission to visit may be required. Call ahead and ask.
• Observe from a safe distance: With leeches inhabiting the pool, you would not want to interact with them.
• Wear protective gear: Given the leeches and the pool's different chemical composition, being cautious is vital.