Las Vegas residents pray for snow after drought

Lake Mead: the tidemark shows the previous and current high-water levels the lake has shrunk to its lowest point since it was first filled in the 1930s Picture: AP

Officials from nearby Las Vegas are pushing conservation, but are also drilling a new pipeline to keep drawing water from the lake.

Hundreds of miles away, farmers who receive water from the lake behind the Hoover Dam are preparing for the worst.

The receding shoreline at one of the main reservoirs in the vast Colorado River water system is raising concerns about a network serving a perennially parched region that is home to 40 million people and four million acres (1.6 million hectares) of farmland.

Marina operators, water managers and farmers who for decades have chased every drop of water across the booming south-west and part of Mexico are closely tracking the reservoir’s water level – which is already at its lowest point since it was first filled in the 1930s.

“We just hope for snow and rain up in Colorado, so it’ll come our way,” said marina operator Steve Biggs, referring to precipitation in the Rockies that flows down the Colorado River to help fill the reservoir separating Nevada and Arizona.

By 2016, continued drought could trigger cuts in water deliveries to both states.

While authorities have said they have been saving water for potential dry days, the prospect of the first cuts is already prompting action.

Last week, officials announced an $11 million (£6.5m) pilot programme involving the federal government and water agencies in Denver, Los Angeles, Las Vegas and Phoenix to pay farmers, cities and industries to reduce river water use.

“We can certainly hope for better conditions than we’ve experienced in recent times, but we have to actively and continue to plan for the worst case,” said Michael J Lacey, director of the Arizona Department of Water Resources.

This week, an update from the federal bureau of reclamation, the keeper of the Colorado River network’s dams and reservoirs, will help set the course for water deliveries for the next two years.

Administrators said they are confident they can meet current commitments next year. Federal officials and water administrators in metro areas such as Las Vegas and Phoenix said they are committed to finding new ways to make every drop of river water count, from cloud seeding to pipelines to new reservoirs to desalination plants.

But they are all watching Lake Mead, the biggest in a Colorado River basin that supplies water to California, Arizona, Colorado, New Mexico, Nevada, Utah, Wyoming and part of Mexico.

The states get annual allotments dating back to the Colorado River Compact of 1922.

Over the years, the amount has not kept pace with a post-Second World War development boom in the south-west, and the drought has increased the pressure.

The lake is expected to drop to 1,080ft (330m) above sea level this year – down almost the width of a football field from a high of 1,225ft in 1983.

A projected level of 1,075ft in January 2016 would trigger cuts in water deliveries to Arizona and Nevada.

At 1,000ft (300m), drinking water intakes would go dry to Las Vegas, a city of two million residents and a destination for 40 million tourists per year that is almost completely dependent on the reservoir.

That has the Southern Nevada Water Authority spending more than $800m to build a 20-foot-(6.1m) diameter pipe so it can keep getting water.

The region is also stressing water conservation, prohibiting grass lawns for new homes and fountains at businesses.