I suspect that the river was a more forgiving landing area.
a couple of friends who are pilots disagree
"As a light aircraft pilot, I can try to answer a more specific question: if your aircraft has a total engine failure, are you more likely to survive over land or sea? And the answer to this is that, generally, you are much more likely to survive over land.
If you suffer a total engine failure, your plane becomes a great big glider. Over land, you would select a field beneath you to land in, set the aircraft for the correct gliding speed, and carry out what is not enormously dissimilar from an ordinary landing. This is the sort of thing that is practiced a lot during training, and most pilots would be able, most of the time, to carry out such a landing without serious damage to the plane or occupants.
Over the sea, such a forced landing is called a "ditching", and you do pretty much the same thing, and the chance of survival up till now is broadly similar to that over land. The problem is that, unlike a forced landing in a field, after which you can sit down and relax with a nice cup of tea, after a forced landing in the sea, your troubles are only just starting. In a light aircraft, you have a couple of minutes to get out before the aircraft sinks, and this is not necessarily easy as the pressure from the water will tend to make opening the doors tricky. Once you are out, although legally you will have a lifejacket with you and so presumably won't drown, you have to get yourself rescued before hypothermia sets in: even in the middle of summer, survival times without a liferaft in the open seas are typically just a few hours, and getting a search and rescue helicopter to pick you up can take longer than that, even if S&R already know exactly where you are, which they are highly unlikely to."
...although this case wasn't in the open sea I suspect the problems of landing on water are scarier for pilots