Lake Tahoe, in California and Nevada, is known for its clarity, but 2025 studies show climate-driven clarity loss, as per a web source. Crater, Mono, and Salton face different issues, making Lake Tahoe the correct choice.

Lake Erie, in the USA and Canada (25,700 km²), was studied in 2025 for cyanobacteria toxins impacting water quality, as per a web source. Michigan, Huron, and Ontario face other issues, making Lake Erie the correct choice.

Great Slave Lake, covering 27,200 km² in Canada’s Northwest Territories, had a 20 cm water level rise in 2025, as reported in a web source. Great Bear, Winnipeg, and Reindeer lack this report, making Great Slave Lake the correct choice.

Lake Michigan, covering 58,000 km² in the USA, was studied in 2025 for climate-driven algal blooms, as per a web source. Superior and Huron are binational, Erie has different issues, making Lake Michigan the correct choice.

Lake Huron, in the USA and Canada, covers 59,600 km² and had ancient hunting camps discovered beneath it, with 2025 DNA studies, as per a web source. Superior, Erie, and Ontario lack this finding, making Lake Huron the correct choice.

Lake Superior, in the USA and Canada, is the largest Great Lake by area (82,100 km²), with 2025 studies suggesting its basin formed millions of years ago, as per a web source. Huron, Michigan, and Erie are smaller, making Lake Superior the correct choice.

Hekla, in Iceland, is a highly active volcano monitored for potential 2025 eruptions, as noted in web sources on Iceland’s volcanic activity. Katla, Eyjafjallajökull, and Grímsvötn are also active but less emphasized in 2025, making Hekla the correct choice.

Cumbre Vieja, on La Palma, Canary Islands, Spain, had volcanic ash analyzed in 2025, as reported in web sources. Teide, El Hierro, and Timanfaya are other volcanoes but lack 2025 ash studies, making Cumbre Vieja the correct choice.

Mauna Loa, in Hawaii, USA, is one of the world’s largest volcanoes, with 2025 studies confirming its shared magma source with Kilauea, as per web sources. Mauna Kea and Haleakalā are dormant, Lo‘ihi is underwater, making Mauna Loa the correct choice.

Sakurajima, on Kyushu, Japan, is one of Japan’s most active volcanoes, with 2025 activity reported in X posts. Mount Fuji is iconic but dormant, Aso and Unzen are less active, making Sakurajima the correct choice.