Could dinosaurs swim

No. Dinosaurs never swam and never flew. Some would enter shallow water to catch prey and possibly bathe, but were not adapted for life in the water.

Don't get confused with animals like PlesiOSaurs or Mosasuars, both of which are reptiles NOT dinosaurs. These reptiles did live at the same time as dinosaurs (throughout the Cretaceous).

Remember: All dinosaurs were reptiles, but not all reptiles were dinosaurs. There were marine reptiles and flying reptiles that lived at the same time as dinosaurs.

----------------------------------------------------------------------That's not exactly right. If the questioner means were there any aquatic dinosaurs, then the answer is correct. However, he's asking if any dinosaurs swam, I think some of the hadrosaurs did - maybe to the extent that modern muskrats do. There's pretty good fossil evidence that indicates some of these animals (Trachodon for e.g.) had webbed feet, which would suggest they weren't afraid to get their feet wet. As noted above, the only truly aquatic reptiles that lived during the age of dinosaurs were plesiOSaurs, ichthyosaurs, and mosasaurs. The mosasaurs were just huge Varanid lizards, as the above answer notes. I'm not sure how the plesiOSaurs or ichthyosaurs are currently classified, but they're definitely not dinosaurs.