Sakhalin Energy is majority-owned by the Shell Group energy corporation and aims to deliver 150,000 barrels of oil a day and 9.6 million metric tons (10.6 million tons) of liquefied natural gas a year.
The development, due to be completed next year, includes a drilling platform, gas plant, export facilities, and some 500 miles (800 kilometers) of oil and gas pipelines, which will cross about a thousand rivers and streams.
Western gray whales migrate to seas off northeast Sakhalin each summer to feed. The island's rivers are important spawning grounds for salmon species.
James Leaton, extractive-industries policy officer for WWF, says there's a 24 percent chance of an oil spill during the lifetime of the project.
He says wildlife experts are also concerned about underwater noise levels during construction, which at times exceeded 140 decibels last yearlouder than the typical thunderclap.
And while Sakhalin Energy had marine mammal experts on hand to monitor how whales reacted to construction noise, weather conditions made the animals difficult to spot.
"When the platform was put up, for example, it was completely foggy, and [whale monitors] couldn't see more than a couple of hundred meters," or about 700 feet, Leaton said.
He says Sakhalin Energy is proceeding with its construction schedule despite a lack of information about how the whales are reacting.
"This is the only known feeding area for western gray whales, so if they're displaced or are stressed by the noise, they may not get enough food to survive the winter," Leaton added.
WWF also says the laying of underground pipelines on Sakhalin has damaged and diverted rivers, causing erosion and clouding them with sediments which could prevent salmon from laying their eggs.
Sakhalin Energy denies its activities are environmentally damaging or that an oil spill incident would be difficult to respond to.
Ivan Chernyakhovskiy, spokesperson for the company, says the sea ice off Sakhalin does not form a single solid sheet but contains numerous open "leads" in which spilt oil could accumulate.
"Oil can be recovered from these," he said. "While ice cover can restrict access to oiled areas, shorebound ice may also act to prevent oiling of shorelines by marine spills."
In the case of oil trapped under ice, Chernyakhovskiy says Sakhalin Energy's ice-breaking standby vessels can break through the ice and bring oil to the surface for recovery.
He says the company is also working alongside a team of leading whale scientiststhe Western Gray Whales Advisory Panel, which was established by the energy companyto manage risks that might harm the animals.
Following advice from the panel, Sakhalin Energy changed the route of its offshore section of pipeline in 2005 to avoid the whales' feeding area, Chernyakhovskiy said.
"From the data we have analyzed to date, there is no obvious difference in distribution, abundance, or behavior of the whales, so an immediate short-term impact has not occurred," he added.
And of the salmon rivers that so far could be affected by new pipelines, less than 2 percent of spawning grounds could potentially be impacted, he said.
Shell Group, the Anglo-Dutch oil giant leading the project, is currently seeking a loan worth 300 million U.S. dollars from the European Bank of Reconstruction and Development to help fund the Sakhalin development.
But campaigners say this funding should be blocked, insisting environmental concerns have yet to be properly addressed.
"Shell is blatantly ignoring international concern and scientific advice," said Andy Ottaway, director of Campaign Whale, based in Lewes, England.
"It would be scandalous if public funds were used to back this project," he added.
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES