FIELD FILE · ILIAMNA-LAKE-MONSTERLAKE & SEA MONSTERREGIONAL LEGEND

Iliamna Lake Monster

Also known as Illie, The Lake Iliamna Monster

“Illie,” a giant fish-like creature reported by bush pilots and villagers in Iliamna Lake, Alaska’s largest lake, since the 1940s.

Iliamna Lake is Alaska’s largest lake – about 77 miles long, up to 22 miles wide and nearly 1,000 feet deep at its deepest – set at the head of the Alaska Peninsula west of Cook Inlet. Its villages, including Iliamna, Newhalen, Kokhanok, Pedro Bay and Igiugig, are reached mostly by small plane or boat, and the lake feeds one of the world’s greatest sockeye salmon runs. It is also home to “Illie,” the most famous lake monster in Alaska.

The lake’s own name may hint at older stories. An early U.S. Geological Survey geologist, G. C. Martin, recorded that Iliamna was said to be the name of a mythical great blackfish living in the lake, which bit holes in the skin boats of wrongdoers – though the name is usually traced to a Dena’ina Athabascan term, Nila Vena, meaning “islands lake.” Local residents have long told of something large in the water, and modern writers often point to those stories as the legend’s roots.

The modern legend took off with aviation. In 1942 bush pilot Babe Alsworth and a passenger, Bill Hammersley, reported seeing huge, dull, aluminum-colored fish from the air – shapes so large they briefly looked like boats. Over the following decades pilots, missionaries, biologists and fishermen added reports of fish 10 to 30 feet long, some with prominent fins. Texas millionaire and monster-hunter Tom Slick hired Alsworth to search the lake from the air in 1959 without result, and around 1979 the Anchorage Daily News offered a reported $100,000 for clear proof. No one ever collected it.

Illie returned to the news in June 2017, when residents of Kokhanok described three large, dark, whale-like backs surfacing and diving for around 40 minutes a few miles offshore. Gary Nielson, one of the witnesses, told a reporter the largest was about twice the length of a 32-foot fishing boat – and that it was too big to approach in a skiff. Like earlier sightings, it ended without photographs that settled anything.

Type

Lake & sea monster

Status

Regional legend

First reported

1942

Best-known location

Iliamna Lake, southwest Alaska

Also called

Illie, The Lake Iliamna Monster

Reported in

Alaska

What witnesses describe

Usually a very large fish, 10–30 feet long or more, with a long, dull silver or aluminum-colored body; some reports describe a dark back, a tall dorsal fin, or a black fin with a white stripe. The 2017 Kokhanok witnesses described dark gray, whale-like backs with no visible head, tail or dorsal fin.

Where and when it’s seen

The deep, cold open water of Iliamna Lake, often seen from the air by pilots on clear days, and near the villages and islands of the southern and eastern shore such as Kokhanok and Pedro Bay. Most reports come from summer, when the lake is free of ice.

Notable sightings

1. 1942Pilots spot giant fish Iliamna Lake, Alaska

   Bush pilot Babe Alsworth and passenger Bill Hammersley reported several enormous, dull aluminum-colored fish below their plane. Theirs is usually counted as the first modern report of Illie.

2. 1959Tom Slick’s aerial search Iliamna Lake

   Adventurer Tom Slick, who also funded Yeti expeditions, hired Alsworth to fly over the lake searching for the creature. Nothing was seen.

3. c. 1979A $100,000 reward Anchorage, Alaska

   The Anchorage Daily News reportedly offered $100,000 for convincing evidence of the creature’s existence. Accounts differ on the exact year and amount, but the prize was never claimed.

4. May 2012The sleeper shark theory Alaska

   Biologist Bruce Wright of the Aleutian Pribilof Islands Association suggested Illie might be a Pacific sleeper shark that had entered the lake, while acknowledging no one knows whether the sharks can live in fresh water.

5. June 19, 2017Three backs off Kokhanok Near Kokhanok, Iliamna Lake

   About nine adults and several children watched three large, dark shapes surface and dive for roughly 40 minutes in the evening. The witnesses reported no heads, tails or dorsal fins.

What could explain it?

• White sturgeon, which can exceed 15–20 feet and live a very long time, fit many descriptions of huge, silvery, finned fish; River Monsters host Jeremy Wade and author Matthew Bille favored this idea, though no sturgeon population is known in the lake.
• The Pacific sleeper shark has been proposed, but it is a saltwater species with a very low dorsal fin, and no freshwater population is known.
• Iliamna has one of the world’s few populations of freshwater harbor seals; a group surfacing together could look like a single large animal.
• Large lake trout, schools of salmon, floating logs and wind-driven waves can all be misjudged at a distance or from the air.

Legend, culture and tourism

Illie is part of the identity of the Iliamna Lake villages, where the creature turns up in local storytelling, news coverage and visitors’ questions. The lake is a homeland for Dena’ina Athabascan, Yup’ik and Alutiiq communities, whose deep knowledge of its waters long predates the monster stories, and much of the region is now part of the Lake Clark National Park and Preserve area.

Places to visit

Where it’s reported

Alaska

Iliamna Lake Monster in the news

No recent headlines about the Iliamna Lake Monster. Our news desk checks every day — see all cryptid news.

First published October 13, 2026 · Updated October 14, 2026