Bristol Bay Commercial fishing at the height of the wild sockeye run in Alaska’s Bristol Bay. © Kai Raymond

Stories in Alaska

With Science as Our Guide

We’re assessing the risk of tailings dam failure in Bristol Bay salmon headwaters.

From the beginning, when a group of inspired ecologists founded The Nature Conservancy 65 years ago, we’ve relied on the best available science to guide us. And when the best-available isn’t good enough, we roll up our sleeves and get to work.

Recently in Alaska’s Bristol Bay, we sought to answer urgent questions about tailings dam safety that went overlooked by regulatory agencies.

In partnership with a commercial fishing trade group, the Bristol Bay Regional Seafood Development Association, we turned to the best tech tools available to assess the risk of developing the proposed large-scale Pebble mine in Alaska’s Bristol Bay—home to the largest runs of wild salmon on the planet. The rivers of Bristol Bay have supported a sustainable commercial salmon fishery for four generations—and a local salmon harvest tradition known to date back thousands of years.

Quote: Andy Wink

TNC expertise is helping our industry understand the risk of tailings dam failure in Bristol Bay when the agencies that should be asking the hard questions have simply fallen short.

Executive Director, Bristol Bay Regional Seafood Development Assoc.

Our recent research assesses risk of large-scale mining in Bristol Bay, a the place where clean and free-flowing rivers have long provided a remarkably valuable wild and sustainable fisheries resource. Specifically, we’ve thoroughly reviewed the likelihood of a tailings dam failure in the Bristol Bay headwaters. Among pressing concerns is the possibility of an accidental spill at a massive earthen dam standing more than three times the height of the Statue of Liberty.

This remote region in Alaska is prone to earthquakes and receives 25 percent more annual precipitation than Seattle—these are among the factors compounding the difficulty of developing a large-scale mine and operating safely. In sum, the computer model findings at the core of our investigation show the likelihood of a spill in this location is too risky to be ignored and deserves thorough official review.

Animation of Tailings Dam Failure
Tailings Dam Failure Animation of tailings dam failure created by our computer model.

“As a scientific organization, we’re committed to continually asking questions and testing assumptions,” says Adrianna Muir, TNC’s Director of Conservation in Alaska. “We were pleased to help commercial fishermen address some of their pressing questions about the long-term outlook for headwaters salmon habitat.”

Key results indicate that spilled tailings—consisting largely of rock, mud, water and concentrations of heavy metals—from a dam breach accident could:

  • travel more than 50 miles downstream and likely reach the Nushagak River, which accounts for about a quarter of the planet’s wild sockeye salmon production;
  • spread more than two miles wide across the river valley;
  • fill valley bottoms and spread tailings over salmon nursery habitat;
  • send mudflows through 150 miles of mapped salmon habitat and more than 400 potential salmon streams;
  • continue to flow as far as Bristol Bay, given the fine-grained nature of the spill material, and settle out in the Nushagak River estuary at the fishing port of Dillingham, Alaska.