On October 12, 2006, at approximately 1500 Pacific daylight time, a Sorensen Searey experimental homebuilt amphibious airplane, N9877S, was substantially damaged when it nosed over during a high-speed water taxi near Marysville, Washington. The private pilot, the sole person onboard, was not injured. The builder/owner was operating the airplane under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the cross-country, personal flight. A flight plan had not been filed. The pilot said that he started the day by flying to Lake Washington, Seattle, Washington, where he practiced 7 water landings. He said he was flying back to his home base at Arlington, Washington, when he decided to do a landing in the brackish waters where Steamboat Slough and Ebey Slough came together. He said the water landing went well, but when he continued with a high speed taxi, the aircraft nosed over. The pilot said that the front of the hull and the cockpit area were fractured and broken. The pilot said that he believes there was a strong tidal current in the area, and it contributed to the aircraft nosing over.