The dried-up delta where the Colorado River once flowed into the sea is stark testament to how demand now outstrips supply on one of the planet’s great rivers.

Colorado-born photographer Peter McBride shared that observation and many others during a Thursday presentation on his book, “The Colorado River: Flowing Through Conflict,” at the fourth annual Visibly Human Symposium.

“Water as medicine” was the theme of this year’s symposium, presented by the Health Sciences Library and the Center for Bioethics and Humanities’ Program for Arts and Humanities in Healthcare. Gov. John Hickenlooper has named 2012 the “Year of Water.”

About 40 people attended McBride’s presentation in the Shore Family Auditorium in the NighthorseCampbell Building.

McBride, a renowned photographer of the world’s remote places, grew up in the Roaring Fork Valley, not far from the headwaters of the Colorado River. He said what began as a childhood curiosity turned into a two-year, 1,500-mile quest to visually document the river from beginning to end.

While the river starts against the majestic backdrop of Rocky Mountain National Park, it doesn’t take long before demands on its water — for agriculture, recreation and thirsty cities across the Southwest — take a harsh toll, noted McBride.

The fast-growing oil and gas industry is suddenly putting even more demands on the river, while 98 percent of the state is suffering from drought, he said. “In my opinion, down the road, we’re going to have to decide if we want food or oil.”

While 80 percent of the precipitation that feeds the river falls on the west side of the Continental Divide, 80 percent of the state’s water users live on the east side, McBride noted.

Diversion projects and massive reservoirs, including Lake Powell, mark the Colorado as it flows toward Mexico. Those reservoirs, which hold four times the annual flow of the river, are drawing down, leaving bathtub rings where water levels once reached.

“We used to have these spikes (in flow),” McBride said. “Now we’re just having a general decline, decline. And all the models point to it getting drier and hotter.”

Despite that, he showed photos that illustrate how the Colorado River is greening pistachio farms and vast lettuce fields — the entire U.S. winter lettuce crop is watered by the river — in arid stretches of desert.

The Colorado Compact (which divvies up the river supply) is based on floods in the early 1900s when the river produced larger flows. Those flows have proven to be an overreach, McBride said. “The Colorado River today is a great testimony to what happens when we ask too much of a limited resource — it disappears.”

He produced a companion film, the award-winning “Chasing Water,” which points out that the Colorado flowed to the sea for 6 million years; but since 1998, it has not. In a clip from the film, McBride paddles a kayak in the river’s sludge pools — “a frappuccino pit,” he calls it — in Mexico.

Despite the Colorado’s dour end and many challenges, the river has hope, he said. The key is awareness of the problem and everybody doing their part.

“We have to get away from that, ‘Oh, it’s their problem downstream.’ We all have to be conscious and conserve our fresh water,” McBride said. “There’s a lot of great things happening around it. The folks in Aurora are doing some great initiatives. Xeriscaping and Smart-scaping is a really good start if you’re curious about how you can make an individual difference.”

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