A cargo plane with engine and landing gear problems made an emergency landing in March on the frozen surface of a lake outside the Estonian capital, authorities said.

One of the six crew members suffered minor injuries and emergency workers were scrambling to empty the plane’s fuel tanks before it polluted the lake, which is the main source of drinking water for Tallinn’s 400,000 residents.

The DHL-chartered Antonov AN26 turboprop aircraft, en route from Finland to Estonia, landed on the ice of Lake Ulemiste just next to Tallinn, Economy Ministry spokesman Kalev Vapper said.

“The plane is lying on the ice now, but it has started to sink slowly,” said Vapper, adding that the plane had incurred minor damage during the landing.

The plane, owned by Polish air cargo company Exin Co. Ltd, was chartered by DHL to fly between Tallinn and the Finnish capital, Helsinki.