Environment Planet Earth 8 Toxic Lakes Where a Dive Could Be Deadly By Josh Lew Josh Lew Writer Metropolitan State University Josh Lew is a freelance writer and copywriter who focuses on travel, green living, and personal finance. Learn about our editorial process Updated June 27, 2021 A dip into Kawah Ijen's highly acidic waters would be deadly. Sumith Nunkham / Getty Images Share Twitter Pinterest Email Environment Weather Outdoors Conservation Nothing beats a refreshing dip in a lake on a hot summer day, but some lakes aren’t as inviting as they may look. Toxic lakes are formed most commonly either on or within proximity to volcanoes. Acidity levels can become so highly concentrated in these lakes, like Costa Rica’s Laguna Caliente, comparable to that of battery acid. In some locations, carbonic acid can saturate a lake such that the gas bursts from the water’s surface and forms a deadly cloud of CO2. Here are eight toxic lakes around the world to avoid swimming in. 1 of 8 Laguna Caliente wiredtourist.com / Flickr / CC BY 2.0 Located 7,545 feet up in the active Poás Volcano in Costa Rica, Laguna Caliente is one lake not worth diving into. With pH levels nearing 0, the famous volcanic crater lake has one of the highest acidity counts of any lake in the world. Sulfur floating on the surface of Laguna Caliente produces a mesmerizing array of colors—from greens and blues to bright yellows. Incredibly, bacteria was discovered in the lake by researchers from the University of Colorado Boulder, suggesting life can survive conditions once thought to be inhospitable. 2 of 8 Lake Nyos Bill Evans, USGS / Wikimedia Commons / Public Domain Situated in the upper reaches of the Oku Volcanic Field in Northwest Cameroon, Lake Nyos poses a threat to all those living beneath its poisonous waters. The carbonic acid-filled waters, one of just three such lakes in the world, are prone to so-called limnic eruptions—when dissolved carbon dioxide burst from the water and form clouds of CO2 overhead. In 1986 one such eruption occurred, killing 1,746 people by asphyxiation. 3 of 8 Lake Kivu Gavin Morrison / Shutterstock The massive 1,040-square-mile Lake Kivu on the border of Rwanda and the Democratic Republic of Congo is much more hospitable to life than Cameroon’s Lake Nyos, but, it, too, has the conditions for deadly limnic eruptions. While some believe that a combination of the lake’s methane and carbon dioxide with nearby volcanic materials could be enough to send the region into chaos, studies show that such a risk is not increasing. 4 of 8 Kawah Ijen R. M. Nunes / Shutterstock High in the rugged mountains of Indonesia’s Ijen volcano complex lies a beautiful, turquoise-colored lake, but taking a dip in its waters would be deadly. Over half a mile wide, the lake, known as Kawah Ijen, is the largest acidic crater lake on the planet. In 2008, Greek-Canadian adventurer George Kourounis took a special rubberized boat onto the waters of Kawah Ijen and measured its pH level at a highly acidic 0.13, near that of battery acid. 5 of 8 Boiling Lake Emily Eriksson / Shutterstock Within Morne Trois National Park on the Caribbean island of Dominica lies the vaporous and deadly Boiling Lake. As its name suggests, parts of the lake are always boiling. Interestingly, Boiling Lake is actually an opening within the Earth’s crust that emits sulfur and other gases, known as a fumarole, that has been flooded. Many visitors to Dominica hike several hours through volcanic terrain to witness the lake's bubbling, grayish waters. 6 of 8 Quilotoa Annom / Wikimedia Commons / Public Domain Nearly 13,000 feet above sea level in the Andes of Ecuador sits the water-filled volcanic crater known as Quilotoa. Formed when the volcano last erupted around 1300 CE, the lake gives off a beautiful greenish hue. Although hiking through the lush rolling hills up to Quilotoa is popular among visitors to the region, getting into the water is not. Perhaps inviting to some, the attractive green water of Quilotoa is highly acidic and quite dangerous. 7 of 8 Lake Natron Richard Mortel / Wikimedia Commons / CC BY 2.0 Lake Natron, within Tanzania's Lake Natron Basin, is a salt lake with average temperatures above 104 degrees. Due to extremely high evaporation levels, the lake is left with abundant amounts of the minerals natron and trona, which give it a pH level over 12. Perhaps the most striking feature of Lake Natron is its occasional red color. This reddish hue can be attributed to the saline-loving bacteria known as cyanobacteria, which creates its own food with photosynthesis and contains a red pigment. Despite its hot temperatures and alkaline makeup, Lake Natron is home to some fish and the endemic lesser flamingo. 8 of 8 Karymsky Lake Yykkaa / Getty Images Nearly four miles south of the Karymsky volcano in eastern Russia lies the acidic Karymsky Lake. The toxic body of water was once a freshwater lake until a dramatic chain of geological events occurred. In January 1996, a nearby earthquake caused violent eruptions from the Karymsky volcano, which was followed by underwater eruptions of lava and gas from the lake itself. Much of the volcanic matter shot up into the air and landed back in the lake, causing its acidity level to rise significantly. The events of early 1996 also resulted in the death of all life within Karymsky Lake, including a large population of kokanee salmon.