FRISCO, Colo. -- Security guards have been hired to help protect Dillon Dam, warning boaters to stay at least 100 feet away from the dam.

The 100-foot rule is not officially in effect yet. Denver Water spokeswoman Stacy Chesney said Denver Water has never allowed boaters to land or anchor on the dam at its mountain reservoir but there hasn't been a rule to keep boaters a certain distance from the dam. She said 100-foot limit won't be enforced until buoys are put in place, which is expected to happen by mid-August.

The guards have been using megaphones to warn people to stay 100 feet away to the surprise of boaters and marina managers.

Frisco Marina manager Phil Hofer said previously he only warned boaters to stay away from one part of the dam. He said marina workers will now have to warn boaters about the change and update their maps.

The road along the 6,000-foot-long earthen dam could also be closed this summer as Denver Water reviews security there.

"There may be more changes that cause closures, but we will be planning these things far in advance and will warn residents as soon as we hear about them," said Craig Austin, Denver Water's safety and security manager.

The federal government has become more concerned about dam security nationally.

In January, two men from Denver were questioned after being spotted on the 6,000-foot-long dam when the road was closed because of bad weather.

The dam, 60 miles west of Denver, is 230 feet high at its tallest point.

The reservoir behind it has a surface area of up to 5 square miles and can hold up to 82 billion gallons of water. It is a popular site for fishing, boating and camping.

Denver Water said the price tag for 24-7 security on Dillon dam is about $350,000 per year.