In the embattled harbours of Odesa, a scientific vessel lists in its mooring. No one has been able to take a look at the damage to the Boris Alexander from Russian drones and shelling that have hit the port city over the past four years of war in Ukraine. It is too dangerous, just as no one has been able to fully monitor the damage the war is doing to the Black Sea.

“We can only wait,” says Dr Jaroslav Slobodnik, the director of the Environmental Institute, headquartered in the Slovak Republic. “The biodiversity landscape is completely altered. A number of species seem to have disappeared, but we need more data. Data which the war makes it impossible to collect.”

Three species of dolphins were living in the Black Sea before the war. Some of the carcasses of poisoned dolphins that have been washing up with regularity along Ukraine’s 1,729-mile-long (2,782km) coastline since the start of the conflict are spotted and counted. About 125 were recorded in the first year of the Russian invasion, and last year scientists documented 49 bodies.

Aside from the oil spills and munitions, accoustic disturbance from military sonar is also thought to be a critical threat to cetaceans, leading to dolphin strandings and death. Sonar use by both ships and submarines is likely to be especially intense around the Kerch Bridge and Russian-controlled areas.

But properly monitoring the mammals, the bellwether of the Black Sea’s health, or to investigate what is killing them, is difficult when there is a war raging. There are fewer people available to count and fewer reports called in by a war-weary Ukrainian population, in addition to the no man’s land of the Crimean peninsula, occupied by Russian forces.

“The dolphins are the sentinels of ecology of the sea, because they are at the top of the food chain,” says Slobodnik. The impact of the “thousands and thousands” of bombs, oil leaks and ships that have been sunk can only be guessed at. “All we can say is that the Black Sea is at a tipping point, perhaps past it, because of this war.”

It has been almost three years since the Kakhovka dam disaster in June 2023, when Russian forces were believed to be behind the sabotage of the structure on the Dnipro River in southern Ukraine. The collapse of the dam killed dozens of people and flooded fields and homes over an area of about 230 sq miles (600 sq km), as well as pouring significant pollutants and heavy metals along the Dnipro into the Black Sea and depositing toxic waste and rotting animal carcasses into the river delta’s sediment.

It was, says Slobodnik, “a toxic punch to the face of the Black Sea”.

Before the Russian invasion in February 2022, Ukraine had been working towards achieving EU environmental standards in its waters and in 2020 had even declared that the Black Sea was “alive” again – after years of its feeder rivers pumping in toxic industrial chemicals and agricultural pesticides. Tens of thousands of euros had been spent on bringing the water purity – and as a result, the biodiversity – up to EU standards.

“It is such a unique ecosystem. I have spent most of my life watching life come back to the Black Sea, pollution reducing, the Danube getting better, so the Black Sea [gets] better. It is my sea. And now this war,” says Slobodnik. “We believe the ecology has been radically changed and damaged. We can see some evidence on satellite imagery; recently, we could see these invasive plants, an ugly, foaming red species.”

Satellite pictures also show dozens of Russian vessels at anchor off the Russian-occupied eastern shores and the Crimean peninsula. Viktor Komorin, a marine scientist at the Ukrainian Scientific Centre of Ecology of the Sea (UkrSCES), says: “We think a lot of the Russian shadow fleet is in and out of there,there have been a lot of sinkings and a lot of damaged vessels, there were a lot of crashes at the beginning of the war near Snake island,all of which are producing oil spills we can see through satellite imagery. But no work can be done on the oil spills; we can only monitor the multiple pollutants – very aggressive and very toxic.”

Komorin has taken part in dozens of scientific expeditions in the Black Sea and fears the war is taking an irreversible toll. “Its a very unique ecosystem, already very vulnerable to climate change and to organic pollution, as 82% of its volume is hydrogen sulphide, where only bacteria thrives. Only the very top surface level of the water is oxygenated water.”

Komorin says he is desperate to discover the reality of the war’s impact on the sea, but he is realistic that the damaged oceanographic research ship the Boris Alexander would be high risk to deploy even if it were seaworthy. “We already know there’s a lot of dangerous objects out there – rockets and mines, drones and other explosives,” he says.

In the meantime, the scientists monitor, worry and wait. Komorin’s institute in Odesa is continuing to build, as best it can, a unique database of environmental DNA from the stomachs of the dolphin carcasses, and is sampling the oils and pollutants turning up along the coastline. He has hopes that a rehabilitation of dolphin numbers could be possible after the war.

“Of course, we have only half our staff left here. Men have gone to the army and women staff with children went abroad. We trust they will return after the war.”