Never enter the river without wearing head protection.
Gath Retractable Visor
Helmet of choice for serious whitewater riverboarders. With the visor down, it's possible to keep your eyes open as you punch through a hole or a wave, giving you that additional split second of sight to spy your next move. Personal experience is that they do get foggy, esp. in cold water. The visor scratches if your hood is not completely clear of debris when you pull down the visor. Visors are replaceable and have an SPF 15.
I used one of these before I bought my own (I bought a retractable) and it was okay, but just a little too big in size. The visor kept falling in front of my face, making it look like I was wearing a mustache. But if you can't afford a retractable go with this one.
Your Basic Brain Bucket
One size fits all. At least they come in pink.