By Stephen Eisenhammer LONDON, May 30 (Reuters) - Protests in northern Peru over the $5 billion Conga gold mine make "no sense" and could spell the end of the project if they succeed in preventing the draining of a nearby lake, the project's junior partner said on Thursday. Tensions flared up again this week over Newmont's proposed mine, with hundreds of protesters taking to the streets and bringing to an end nine months of relative calm. "We are working with the best of intentions. If we can go ahead good, if we cannot that's it... there are no alternatives," Roque Benavides, chief executive of Newmont's partner Buenaventura, told Reuters on the sidelines of a conference in London. Benavides said he did not understand the protests because the planned transfer of water from Lake Perol to a new reservoir had not yet begun. "People may complain but it has no sense," he said. The construction of the mine, which would be Peru's most expensive ever, was put on hold last year until local disputes over water supply could be resolved. Benavides said this approach had not changed. "We are doing our best. We are not mining, we are following the main thing which is water first." A spokesman at Newmont reiterated the "water first" position but would not say whether being unable to drain Lake Perol would be a turning point. In an interview with Reuters last week Benavides said that construction of the mine would begin if the company could pump water from Lake Perol into the second of four reservoirs it is building without sparking broad local opposition. Lake Perol is one of several alpine lakes in Cajamarca that would be affected by the proposed mine, which would essentially extend the life of the nearby Yanacocha mine the two companies run. But protesters told Reuters on Thursday that they would not give up and that plans to occupy Lake Perol on June 17 had already been set. "We won't be happy until the government says the project will not go forward," said community leader Milton Sanchez. President Ollanta Humala has twice shuffled his cabinet since taking office in 2011 in large part because of violent protests over Conga.