Residents of the Russian Arctic city of Norilsk spent time in and around Lake Dolgoye on Tuesday, as temperatures in the region soared. The lake is used for water discharge from Norilsk‘s Central Heating and Power Plant No. 1, but was used for swimming on July 27 as the temperature in the city reached 30 degrees Celsius (86 F).

A spill that dumped thousands of tons of diesel fuel into the Russian Arctic earlier this year was caused by violations during construction and operation of a storage tank, not permafrost melt, according to a preliminary investigation. 

The spill of the fuel-water mixture occurred on the Ambarnaya River in Norilsk during the clean up from the consequences of the accident at the TPP-3.

Toxic fuel from 21,000 ton leak reaches pristine lake, bypassing floating booms, as rivers of diesel pollution cover-up is exposed.

The exact reason of the leak is yet to be established, but a statement from Norilsk Nickel company, which operates the site suggests it could have been caused - worryingly - by collapsing permafrost.

Red water - nickel processing plant says cause is decades of contamination in Soviet times which company is working to overcome.