DECKERS, Colo. -- A massive effort is under way to protect Denver's water supply from fire zone contamination.

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Protecting Cheesman's Water

7NEWS Reporter Lance Hernandez went into the fire zone Thursday at Cheesman Reservoir (pictured, left), the workhorse of Denver's water supply system to find out what water officials are doing to protect the water we drink.

Cheesman Dam was built with hand-carved stone nearly 100 years ago. Behind it sits one of the cleanest lakes in Colorado.

But, Hernandez said that many experts wonder how long it will remain clean.

"We're going to get silt and ash. That's the kind of thing you live with in Colorado," said Rocky Wiley of the Denver Water Board.

You can already see where fire zone run-off is starting to pollute the lake.

The big Hayman Fire didn't just char the forest -- it changed the soil. It's called hydrophobic soil. Water flows over it and doesn't sink in very well

That's why work crews are trying to block some of the drainages so they can keep topsoil from washing down into the lake.

"Cheesman reservoir is Denver Water's last stand," said Wiley. "Any debris that gets past this reservoir ends up in the water treatment plant. That's why they set up buoys two days ago to trap any debris that comes in."

If debris reaches the Strontia Springs Dam, they may have to flush out the valves. But, in this drought, the last thing they want to do is waste that water.

The ash that washed into Cheesman Reservoir is already giving some of Denver's water supply a smoky taste, Hernandez said. But officials say, so far, the overall ash amounts are small.