OSLO, Oct 27 (Reuters) - Vattenfall slumped to an operating profit of 4.7 billion crowns ($538 million) in the third quarter from 8.7 billion crowns a year ago, it said on Tuesday, as an unusually high hydrological balance put pressure on Nordic power prices.

"Price hedges and a positive contribution from the sales operations and trading have counterbalanced the negative effect of lower electricity prices," the utility firm said in a statement.

($1 = 8.7369 Swedish crowns) ($1 = 8.7369 Swedish crowns) (Reporting by Nora Buli, editing by Gwladys Fouche)