Bangladesh is staring at one of its biggest ecological disasters. More than 200,000 litres of oil has spilled into an estuary within the Sundarbans after an oil tanker collided with another boat early on Tuesday morning. The oil slick from the spill has already spread more than 20 km both upstream and downstream from its point of origin on the Shela river.

Bangladesh authorities managed to remove the capsized tanker from the water on Thursday and are in the initial stages of assessing the damage. Reports from the ground indicate the spill has the makings of a major disaster.

The geography of the spill makes a enormous challenge to clean. The tides in the estuary change every six hours and by turns will push the oil both downstream and further upstream into the mangrove forests, spreading the oil quickly. This poses a severe threat to the ecology of the sensitive Sundarbans, a UNESCO world heritage site. Reports are beginning to trickle in about dead fish, crabs and egrets found in the streams and creeks near the spill. Ecologists are concerned that the impacts of the spill could run through the entire Sundarbans. Oil spreading through the mangroves could kill seeds and prevent the forests from regenerating, threatening the whole ecosystem.

Immediate worry

But the most immediate worry is for the Irrawady dolphins. About 6,000 of this endangered species live in the Bangladesh Sundarbans, one of the biggest populations of the marine mammal. In fact, the accident took place within one of three sanctuaries for the dolphin.

“Dolphins are at the top of the food chain so they will be affected sooner or later by eating the fish from these waters,” said Rubaiyat Mansur, Bangladesh head of the Wildlife Conservation Society. Mansur also worries about the more direct impact on the animals. “The oil slick collects at the confluences and meanders of the river and those are the places that the dolphins like to hang around in and look for prey," he said. "Coming up in an oil slick, opening a blow hole and breathing in and breathing out won’t be a good idea because the air right above the oil slick will be quite toxic.”

Anurag Danda, head of the Sundarbans landscape programme in India for the World Wildlife Fund, said he was concerned about are the crustaceans, particularly that crabs, that have a very significant role to play in the mangrove ecosystem. Crabs, which close their burrows and hide within them during the high tide will not be able to open their burrows at night with the oil swashing up on the sand above them. This could result in a large number of crab deaths. Crabs are also instrumental in turning over the wet and sticky soil of the mangroves, which keeps the forests healthy. Their sudden deaths will have a cascading impact through the food chain.

Tiger's fate

Of course, everyone’s worried for that most iconic creature of the Sundarbans – the tiger. For now the tiger seems pretty far removed from the impact of the oil spill. “It is not going to affect the tigers directly because they don’t live on fish only," said Iqbal Hussain, conservation manager with the Bangladesh NGO, Wild Team. "But it will definitely affect their movements. They cross two or three creeks everyday and that’s where the oil get on to their bodies. So there can be longer-term effect.”

The spill is likely to hit communities living in the Sundarbans hard. “The people living around the Sundarbans are some of the poorest people in the country," said Mansur of the Wildlife Conservation Society. "They have come from all over the country in the last 20-30 years.” He predicts that one such community, the shrimp farmers, is going to feel the blow soon. “In the next new moon, when hundreds of shrimp nets come up, I’m sure that they will catch not so many as last time,” he predicts.

Although oil tankers are legally not allowed through the sanctuary waters, they have been using the streams ever since the main route has been blocked by silt. According to Wild Team's Hussain, the Bangladeshi forest departent and water bodies authority have been debating the issue for close to three years but have not found a solution yet.

Take a look at this video of the mess left behind after the 350,000 litre tanker emptied four of its six oil chambers into the mangroves waters.

Video: YouTube/Md. Ashik-Ur Rahman