Not every marine ecosystem gets a second chance. Fewer still get ruined twice.

But Howe Sound, where an environmental rebirth has been unfolding for the past eight years, may soon start to slide back toward environmental sterility.

Could we really blow it twice? Ruth Simons, executive director of the Future of Howe Sound Society, hopes not – but she fears the worst.

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"When you look at how fortunate we are … it would really be sad to let that slip away [again]," she says. "My biggest fear is that irreversible projects, projects that are not renewable, that are not going to benefit the region, go ahead. And once it's gone, it's gone."

Gone again, that is. It seemed like it was gone forever several decades ago when the cumulative impact of pollution from pulp mills and acid drainage from an abandoned copper mine left the waters of Howe Sound largely lifeless.

The seabed near the Britannia Beach mine was described as "a moonscape" by divers who went down looking for marine life after the mine closed in 1974. They couldn't even find algae.

Across the sound at Port Mellon, a pulp mill that started up in 1909 had drained so much sulphate into the waters that by the 1980s, the crab fishery was closed.

A once-thriving commercial prawn fishery also shut down throughout Howe Sound because there was so little to catch. Salmon stopped running into many of the smaller streams. And the herring, which once spawned in great swirling schools, simply vanished.

The first glimmer of hope came in 1988 when Howe Sound Pulp and Paper began a $1.3-billion renewal process at Port Mellon. The project would turn what was openly recognized as an environmental disaster into one of the most modern, cleanest pulp mills in the world.

Then, in 2004, the provincial government joined the fight, making a pivotal decision to build a long discussed water-treatment plant at the old Britannia Beach mine site. Under the direction of EPCOR, a $15-million facility was soon filtering out sulphide-bearing heavy metals and pumping clean water into Britannia Creek, which flowed into Howe Sound. In 2011, salmon returned to spawn in the once-dead stream – and they have kept coming back since.

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Crabs and prawns are again being caught throughout Howe Sound.

In 2006, the Squamish Streamkeepers Society began working with Squamish Terminals to wrap protective coverings on creosote-covered wood pilings at the docks. The move allowed herring eggs to survive and sparked a return of the small fish. That had big repercussions. Soon, schools of hundreds of dolphins were pursuing herring through Howe Sound. Last spring, killer whales were seen in the waters that glisten below the Sea-to-Sky Highway and in September, the Squamish River had so many salmon that for the first time in 50 years commercial fishing was allowed. In two days, four boats caught 300,000 pink salmon.

Last week, the latest – and single biggest – sign of revival came when a humpback whale travelled up the fjord, breaching along the way.

But no sooner had Howe Sound come back to life than industrial projects again emerged as threats. An LNG facility is proposed on the site of the old Woodfibre pulp mill, which closed in 2006.

Logging is expanding on some of the islands. And a Calgary company is pushing to develop a huge gravel mine at the mouth of McNabb Creek, an important salmon spawning stream. Meanwhile, a proposal by the Future of Howe Sound Society to create a protected area in the heart of the Sound is largely being ignored by authorities.

"I think the province and the federal government need to realize the social and economic value of this particular area," Ms. Simons says. "And the public needs to be more vocal about it … I think it's one of those areas that we take for granted."

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We certainly did once. And look what happened. Even the algae died. Now we've got it back, but without an overall plan to protect the area it will be lost again.