Russia officials have been left scratching their heads after thousands of dead fish washed up on the shores for the second time in week.s
The sea creatures have washed up on the shores of a reservoir in a southern Russia creating a smelly mass grave.
The unexplained phenomenon has sparked a probe by investigators.
It has prompted fears of an environmental disaster with some believing the catastrophe is due to a drop in water levels.
Witnesses filmed the stark scene which saw hoards of lifeless fish on the sandbanks next to Arshan-Zelmen reservoir.
One said it had an “absolutely terrible” smell and pointed to emissions from a nearby factory, The Moscow Times reported.
An investigation has been launched into mass-deaths with prosecutors believing it is the result of a critical drop in water levels.
Both the Investigative Committee and the regional prosecutors’ office said they will determine the next course of action based on initial probes.
It is not the first fish death to hit the headlines in recent weeks.
In October swathes of lifeless aquatic creatures washed up on the coast in Kamchatka.
Fish, octopuses, seals and sea urchins were found lifeless after an unexplained phenomena wiped out 95% of marine life.
Rocket fuel has been blamed for polluting the water, promoting feats that supplies stored in military testing grounds may have leaked.
The first test site, Radygino, is about six miles (10km) from the sea and was used for drills in August, The Guardian reported.
Greenpeace, which has been assessing the area, warned of an “ecological disaster”.
It comes following a massive diesel fuel spill in the arctic and large-scale wildfires in Siberia, marking a tough environmental year for Russia.