The agency that is lining a border waterway with concrete agreed Tuesday to consider adding ladders and buoys to prevent migrants from drowning when they illegally cross from Mexico into Southern California.

The Imperial Irrigation District is having second thoughts about whether designs for 23 concrete-lined miles of the All-American Canal offer enough protections against drownings. The 80-mile waterway has claimed more than 500 lives since it was built in 1942. The project to limit water seepage will deepen the canal and make the current faster.

The district's board, meeting in El Centro, voted unanimously to ask its partner on the project, the San Diego County Water Authority, to consider buoys and ladders on both sides of the waterway, spaced 150 feet apart along the concrete lining. Patches of bolted, synthetic cleats would make it easier for humans and animals to climb out, and a 10-foot fence would be constructed to keep migrants away from the waterway.

The changes would represent a mid-construction shift on the $285 million project, which began in July 2007 and is scheduled to finish in 2010. Current plans call for installing ladders every 250 feet on alternating sides.

"(It) is the clear sentiment of this board that more can and should be done to safeguard human life than has been the case to this point in the construction process," the board wrote to San Diego authorities.

The district's shift is a modest victory for the unusual alliance of Rep. Duncan Hunter, R-Calif., and his brother, John, who has installed water jugs in the Southern California desert since the late 1990s to aid dehydrated border crossers.

"We won the fifth round," said John Hunter, who last month showed the board video testimonials of families who lost loved ones in the canal. "We still have 10 rounds to go."

The San Diego County Water Authority, which is paying for much of the project, believes the measures may encourage migrants to cross illegally, said Halla Razak, the agency's Colorado River programs director.

"We believe these kind of measures just provide a false sense of security," she said. "The canal should not appear like a swimming pool that people can jump and swim across easily."

The earthen All-American Canal runs close to the U.S.-Mexico border, carrying Colorado River water to vegetable farms in California's Imperial Valley. The concrete lining is expected to capture water for 135,000 homes, mostly in San Diego and its suburbs. That water has been seeping into farms on both sides of the border.

The Imperial Irrigation District is overseeing construction. The San Diego agency and the state of California are splitting the costs.

More than 400 people died in the canal from 1975 through 2006, according to John Hunter. Drownings peaked at 31 in 1998 as heightened enforcement in San Diego pushed migrants east to the deserts of California and Arizona.

The Imperial Irrigation District has resisted pleas from John Hunter since 2001 to add buoys and other safety devices on the canal. Board member Stella Mendoza said Monday she still worries that such measures may make the agency liable for any deaths.

Duncan Hunter, who has staunchly advocated for more border fencing, has criticized the plans for concrete lining for failing to do enough to protect lives.

"The loss of human life in the Canal to date has been a costly consequence to past indifference," he wrote the agency's board in June.