My wife's family lives in Webster City and when the Boone is going off (a river going off in Iowa; Hardee Har har!), there is on old dam type structure close to downtown that turns into a great hole(s).  I about feel out the first time I saw it.  A little shallow, but less so than chompy over at Union chutes here in Denver.  And it is river wide with many breaks in it for easy outs.  It is so old, it looks like a natural feature in terms of variations of the holes.

AND, the USGS page has the river level on its page.
http://webdiaiwc.cr.usgs.gov/rt-cgi/gen_stn_pg?station=05481000

Now that I have an EZ, I will take it with next time I go back home with her and tear up the Boone.  I am actually looking forward to it!

Mike