Land purchases, fences and wildlife crossings have combined to produce a success story for the Central Arizona Project.

The success has been in keeping deer and other wildlife from getting trapped and drowned in the CAP canal that brings Tucson and Phoenix much of their drinking water from the Colorado River.

The deaths were a big problem more than two decades ago during the project's early years, but have been dramatically reduced.

In the last seven years, about the same number of deer died in the entire, 336-mile-long canal as died in a stretch barely half as long back in the early 1980s.

The federal purchase of 4 1/2-square miles of open desert west of the Tucson Mountains was one piece of the fix. The land, spreading south and east of Mile Wide and Sandario roads, was bought in the 1980s to compensate for the canal's environmental effects and to give deer and other wildlife safe places to cross.

There, numerous untrammeled desert washes serve as crossings over the canal, which was built underground in those sections.

Fencing the entire canal, and constructing bridges and other wildlife crossings over it, have also helped.

In the early years of the CAP's construction and operations back in the 1970s and '80s, many deer died in it. Workers would build canal segments, then let water into them before they were fenced.

Gates also would be left open as contractors worked on the project, letting deer in, recalled Henry Messing, a U.S. Bureau of Reclamation biologist in Phoenix who has worked with the project for 24 years. The bureau built the CAP.

From 1979 to 1983, a total of 49 deer were seen inside the first 173 miles of canal, from Lake Havasu to Phoenix, reports Paul Krausman, a professor of wildlife conservation at the University of Montana.

Of those, 21 died, by drowning or heat exposure inside the canal or after they escaped with help.

"The distance from the top of the canal to the water was large. Deer likely attempted to drink and slipped into the canal not being able to escape," said Krausman, a former longtime UA wildlife-ecology professor.

"It doesn't take long with the sun beating down on you in a concrete-lined canal" to suffer from the heat, he said.

But after the federal government bought the 4 1/2-square miles in the Tucson Mountains, Krausman and other UA researchers did a study showing that the property was being used and that deer were making it around or through the canal.

The researchers captured 17 deer, outfitted them with radio collars and followed them for nearly a year in 1996 and 1997 to make that finding.

Officials also built 60 to 70 bridges and other wildlife crossings across the canal from Lake Havasu to Tucson. Although there are no statistics on how many deer crossed them, it is clear that some did, Krausman and Messing said.

Finally, after completion, the canal was lined with fencing for nearly $10 million. Since then, the fence has worked but isn't foolproof, with animals continuing to slip into the canal through open gates or by jumping over or digging under fencing.

From 2003 through early this year, 54 deer entered the entire 336-mile CAP canal, Krausman reports in a new study. Twenty-three died.

In all, 216 animals, including dogs, cats, snakes, burros, javelinas, hawks, coyotes, sheep and cattle made it through the fencing during those years. Of those, 49 died, but Messing said the death toll would have been much higher without fences.

To make sure people and animals don't get in, a crew of six spends about $180,000 of the project's $700,000 annual budget in the Tucson canal area on maintenance work, said John Officer, supervisor of CAP's canal system here.

"We get holes every week," he said. "Vandalism creates holes. People want to see what's on the other side."

BY THE NUMBERS

• From 1979 to 1983, while the Central Arizona Project was under construction, 49 deer got into the unfenced canal, and 21 died in the 173-mile stretch from the Colorado River to Phoenix.

• From 2003 to early 2010, 54 deer got into the 336-mile fenced canal from the river to Tucson, and 23 died.

Sources: Central Arizona Project and professor Paul Krausman of the University of Montana.

Contact reporter Tony Davis at 806-7746 or tdavis@azstarnet.com