Ullum Reservoir

The Dique de Ullum holds back the San Juan river in a narrow gap between bare desert ranges, and the result is a sheet of deep blue water surrounded by rock the colour of ash and rust, with no vegetation to soften the contrast. Being twenty minutes from the provincial capital, it is where San Juan swims, sails and waterskis: clubs and beaches line the eastern shore, boats and jet skis run in summer, and there are viewpoints on the road above the dam wall looking down the length of the lake. Wind picks up in the afternoon, which suits sailing and windsurfing. It is a practical, popular place rather than a wild one, and it fills to bursting on hot weekends.

What you actually see

• The blue lake - deep water against bare desert mountains.
• The beach clubs - swimming areas and services along the eastern shore.
• The dam viewpoint - the road above the wall looking down the reservoir.
• The sailing - boats and boards on the afternoon wind.

When to go

October to April for warm water and full services; December to February is the busiest and hottest, with temperatures often above thirty-five degrees. Winter is quiet, cold and windy, with most services closed.

Honest expectations

The shoreline is developed with clubs, parking and kiosks rather than natural beach, and litter can be an issue after busy weekends. There is no shade anywhere. Water levels vary with irrigation demand through the season.

Nearby

San Juan city is twenty minutes east; the Zonda valley and wineries lie nearby.