To repeat earlier comments, I do not think that either "keepnet", "tureens" or "cribble" is the solution to 99.
Why not?
Firstly, none of them gives me that "fits perfectly" feeling. Keepnet is too literal, and it is not suspended OVER a river but IN a river - or lake, or pond, etc. The clues are always too clever for this.
My best thought at the moment is that it is a word for "Hold on to" and/or "catch" straddling a short word for a river (perhaps either "r" or a real river somewhere). Many people have suggested Ure for the river, with "net" and "s" leading them to "tureens" but I am afraid that I find this unconvincing too.
"Cribble" is not a container, as I understand Chambers.
I am sorry to be negative and admit that I may be wrong, given that I do not have an answer to this, my last, clue. It is now difficult to think laterally with these words banging around in my brain!