powerful tides and currents, which suck the baby salmon down.) Another conservation effort that has helped the salmon recover is the destruction of old, outdated dams, such as the Lewiston Dam on the Clearwater River, a tributary of the Snake. After destroying the dam, salmon populations noticeably recovered. Another recovery method carried out by the Corps of Engineers is called Fish Transportation. Since many juvenile salmon perish at each dam while swimming out to the ocean, ships filter and collect these salmon smolts by size and take them out to the ocean, where they can be guaranteed to make it alive to saltwater. This method raises controversy to the effectiveness and costs, since this method is extremely expensive, almost costing $15 million. Another possible upstream passage solution is the Whooshh Fish Transport System. Engineers at Whooshh Innovations have developed a fish passage system that allows for the safe and timely transportation of fish over barriers through a flexible tube system via volitional entry into the system. Overall, these combined efforts have had good success. In the summer of 2006, the Snake River reportedly only had 3 sockeye salmon that returned to their spawning grounds. In the summer of 2013, more than 13,000 sockeye salmon returned to the spawning grounds. Navigation In the 1960s and 1970s the U.S. Army Corps of Engineers built four dams and locks on the lower Snake River to facilitate shipping. The lower Columbia River has likewise been dammed for navigation. Thus a deep shipping channel through locks and slackwater reservoirs for heavy barges exists from the Pacific Ocean to Lewiston, Idaho. Most barge traffic originating on the Snake River goes to deep-water ports on the lower Columbia River, such as Portland. Grain, mostly wheat, is the main product shipped from the Snake, and nearly all of it is exported internationally from the lower Columbia River ports. The shipping channel is authorized to be at least deep and wide. Where river depths were less than , the shipping channel has been dredged in most places. Dredging and redredging work is ongoing and actual depths vary over time. With a channel about deeper than the Mississippi River system, the Columbia and Snake rivers can float barges twice as heavy. Agricultural products from Idaho and eastern Washington are among the main goods transported by barge on the Snake and Columbia rivers. Grain, mainly wheat, accounts for more than 85%