Surface water InSAR is a new and challenging field of SAR application that involves studies of water level change in flood plains, wetlands and coastal regions. Heretofore such studies have been mainly carried using L-band SAR observations. These studies show spatially detailed, quantitative images of water levels that can be never obtained from in-situ measurements at only several stations. Unlike successful results acquired from L-band interferometry, it is deemed that C-band interferometry does not work in inundated vegetation areas. However, we recently found that C-band interferograms (ERS-1/2 and RADARSAT-1) with short acquisition time intervals can maintain excellent coherence over the Everglades and Louisiana wetlands, and disclose water level changes beneath tree or saw grass. In addition, in some regions such as "Manchac" Swamps, Louisiana, coherence was maintained over three year period. Our results also show that RADARSAT-1 provides better results than ERS with respect to temporal decorrelation.