BEVERLY - Various subspecies of salmon and the seagoing trout called steelhead are at the mouth of Columbia River. They're making their way to the spawning grounds in inland streams.

The question is, how to get them there.

Of course they swim. But the river is full of obstacles, always has been, and some of the man-made ones are big. The answer was worked out decades ago, when the hydropower projects along the Columbia River were being constructed. They've been fine-tuned since then with strategies like remodeled fish ladders, updated strategies for hatchery management and a hole cut in the dam.

What's new is water slides for baby fish. Technically that concept is old too - the chunk cut out of Wanapum Dam is a baby fish water slide - but the water slides at Priest Rapids Dam are new.

They're technically spillways that have been remodeled to accommodate passage of juvenile fish downstream.

It's all a function of juvenile fish behavior, Curt Dotson, fisheries program supervisor for the Grant County PUD, said. The PUD owns both Priest Rapids and Wanapum dams.

Baby salmon and steelhead usually swim in the top 20 feet of water, Dotson said. So the best way to persuade them to take the least injurious way downstream is to devise a system that lets them stay in the top 20 to 25 feet of water. Hence the water slides.

"At Wanapum, we cut a hole right through the dam," Dotson said. That project was completed in 2008, according to the PUD website. Juveniles ride the current through the fish bypass gate and "boom, straight down they go," Dotson said.

Each of the three Priest Rapids gates is 44 feet wide and the slide is 204 feet, according to information from the PUD. Construction began in August 2011 and was completed in April. Project cost was $29 million.

Previously the dam operators had to open all the spillway gates during juvenile fish passage, Dotson said. Now more water can be captured for power generation. "What we paid to build these things, (in) five to seven years we'll get our money back," he said.

The PUD also has to get adult fish upstream to the spawning grounds, and that has proved a bit more problematic this year. That's because there is a bit of a problem at Wanapum.

A crack in one of the spillway pillars was discovered on Feb. 27. Utility district officials dropped the water level, which closed the crack. A subsequent investigation determined there was a calculation error during the design phase.

The PUD has come up with a plan to fix the problem, but in the meantime river levels remain well below normal. That's been a problem for, among others, the fish trying to travel upstream.

Normally the adult fish would climb the ladder (which really does ascend like a set of stairs) and then swim out the opening at the upstream side. Not now. With the low water it's a long way from that opening down to the water.

Regulations of various agencies require that everything be ready for the upstream migration by April 1. The water was lowered Feb. 28. Utility district officials had about 31 days to figure out what to do.

The technique of getting fish upstream is pretty well established, "a proven technology over decades," public affairs officer Chuck Allen said. Dropping the river level was a "unique situation," he said.

To address that unique situation PUD officials came up with a slightly different water slide, And not just a water slide - it has one of those curving tubes that dump the fish back in the river.

After climbing the fish ladder, there's a ramp partitioned into channels, which funnels them into the curving tube. They pop out of the tube at river level.

The repairs to Wanapum Dam should be completed and the pool behind the dam refilled by the end of the year, according to PUD officials.