Willfull suspension of disbelief as it pertains to river play

[B Dids]

Party 5/10

Fishy limps UTG he was the 43/5 type...

I raise K [img]/images/graemlins/diamond.gif[/img] 9 [img]/images/graemlins/diamond.gif[/img] next to act.

Solidish if slightly passive preflop player (~25/11) 3 bets me.

Loose passive OTB calls three cold.

Blinds fold, UTG calls, I call.

Flop K [img]/images/graemlins/spade.gif[/img] 9 [img]/images/graemlins/heart.gif[/img] 7 [img]/images/graemlins/spade.gif[/img]

UTG checks, I check, Preflop raiser bets, button calls, UTG calls, I raise, they call call.

Turn 4 [img]/images/graemlins/spade.gif[/img]

Checked to me, I bet, pfr folds, button and UTG call.

River 4 [img]/images/graemlins/heart.gif[/img]

UTG bets out, what's my move here?

UTG could have a 4, but he sure doesn't have to. The button is a calling station and he could easily overcall if I decline to raise. There's a slimmer change he'd call two cold anyway. Your thoughts?