Historically late March is the best time to float if you are planning in advance. Most likely chance of water with reasonable weather. Not sure about ice, but looks like it runs much of the winter if you are really into suffering.
We carried all of our water, but the best source that we saw was angel cove spring. This is a 5 minute hike from the river. Bull canyon had a little flowing water, but seemed to have an oil sheen, probably from a natural seep.
Life is either a daring adventure or nothing. - Helen Keller