The tusk was identified and authenticated by officials at the Burke Museum of Natural History and Culture, who were called to the scene immediately after the discovery was made.
"Burke Museum paleontologists have examined the fossil and we are confident that it represents a tusk from an ice age mammoth,” Christian Sidor, curator of vertebrate paleontology, told local news station Q13 Fox.
“The discovery of a mammoth tusk in South Lake Union is a rare opportunity to directly study Seattle’s ancient natural history," Sidor added. "As a public repository, the Burke Museum would be pleased to curate the tusk and provide access to scientists and others wishing to study it."
Because the tusk was uncovered on private property, the landowner will have the final decision on what happens to the fossil.
Scientists can't yet pinpoint what species of mammoth the tusk belongs to. Mammoths are a genus of giant mammal ancestors closely related to the modern elephant. They roamed the steppe tundra of Asia and North America in herds some 10,000 years ago.