I've copied this from the bbc report.
Oceanographers here in Western Australia believe that if the debris is from the Malaysia airlines flight it probably crashed about 300-400km to the west due to prevailing currents. The search stretches across 7.7 million sq km - an area larger than the...
The Indian navy have 4 warships searching there.
http://www.newindianexpress.com/world/India-Deploys-4-Warships-to-Locate-Missing-Malaysian-Plane/2014/03/13/article2107391.ece?utm_content=buffer89235&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer#.UyIQuIWFt-w
The plane had only just taken off and was just three miles out, so therefore not very high. The river did tear holes in the fuselage even then but as the emergency services were already alerted, there was enough time to get the passengers and crew off.
A search & rescue team from an American naval ship were on TV, explaining they could find objects as small as a football, so if there was a small piece of wreckage, it would have been detected.