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Visitors afloat on Crystal Lake in the Frozen Niagara section of Mammoth Cave. Mammoth Cave collection.
For about a hundred years, visitors have boated on or walked past Crystal Lake in the Frozen Niagara section of Mammoth Cave. Most left only footprints, but some left trash — and one left a Ninja Turtle. Park resource managers set out to clean the lake and return it to a more natural state.
A lake built for a boat tour
Crystal Lake is a small natural pond held back by a stone embankment, beneath Moonlight Dome, a 35-foot dome that trickles in wet weather and is hung with flowstone cascades and draperies.
In 1923 the cave operator George Morrison enlarged it with a concrete dam, so he could offer boat tours in his section of the cave and compete with the Echo River boat tours of the Mammoth Cave Estate below. Visitors climbed down wooden stairs to a 3-by-11-foot concrete landing. The ride was said to be so short that you could push off one side and bump the other — but it let Morrison advertise a "boat tour". The lake stayed in use through his ownership and after the land passed to the federal government in 1941.
Crystal Lake from above in the 1950s. Mammoth Cave collection.
A new trail — and a chance to clean
In November 2022 the park began a year-long rebuild of about one mile of cave trail from the New Entrance to Frozen Niagara: harder trail surfaces, curbs, stainless steel handrails, rebuilt stairs, and new overlooks and seats. At Crystal Lake, where the old walkway gave no clear view, a see-through metal grate now extends out over the water.
The work closed the area for almost 12 months, so managers took the chance to clear out a century of trash. Removing copper pennies and other metals — and the old underwater tour lights — could make the lake habitable again for cave crayfish and cave shrimp, absent for years; heavy metals can harm sensitive cave life.
Student Conservation Association interns monitor the water level as the lake is drained. NPS photo.
Draining a lake underground
Scientists set up a siphon and an electric pump to move water over the old dam. It took weeks, because rain on the surface kept draining into the cave and raising the level. They learned the lake collects water from only about 5,000 square feet — about 0.1 acre — of land above.
Lowered by about 9 feet, the lake bottom was finally within reach. Eighteen members of the National Speleological Society volunteered 108 hours, carrying 120 bucket loads — roughly two tons of mud — to the surface, then screening it for trash.
Members of the park's science and resource management team on the bottom of Crystal Lake. NPS photo.
What they found
Coins and chewed bubble gum — about 200 grams of it — were the most common finds. Cameras, flashbulbs, flashlights and hats had probably slipped from people leaning over the rail for the perfect photo. A golf ball and a plastic spoon raise questions.
| Kind | Items |
|---|---|
| Coins | 1 cent to 50 cents; the oldest a 1934 quarter, then 90 percent silver |
| Camera items | flashcubes of various styles, a digital camera, a roll of Kodacolor II film |
| Clothing | hats, reading glasses, Oakley sunglasses |
| Bottles | glass Coke bottles and others |
| Other | flashlights, an Edgeworth tobacco tin, a golf ball, a bouncy ball, a plastic spoon, and Raphael, the Teenage Mutant Ninja Turtle — missing a leg and both forearms |
Some of the finds, including the Ninja Turtle. NPS photo.
Glass bottles from the lake bottom. NPS photo.
Keeping the cave healthy
Clean-ups like this help keep Mammoth Cave's ecosystems healthy. Volunteer groups carry out hundreds of pounds of old broken concrete, unused lighting cable and treated wood by hand, and specially trained staff rappel into deep pits to retrieve things visitors have dropped. All of it helps return the cave to a more natural home for the creatures that depend on it.
Sources
- National Park Service, Mammoth Cave National Park, "Crystal Lake Cleanup at Mammoth Cave." https://www.nps.gov/maca/crystal-lake-cleanup.htm
- Cave trail rehabilitation project: https://www.nps.gov/articles/000/cave-trail-project-new-entrance-to-frozen-niagara.htm
- The original calls the interns' programme the "Student Conservation Corps (SCA)"; SCA is the Student Conservation Association.
- Rewritten in hubnx's own words.
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