hit backdoor flush, very bad board, action?

[sxz18]

2/4 NL on FTP

Hero ($180)
BB ($450)
MP ($110)
MP1 ($120)

Hero is dealt 9 [img]/images/graemlins/heart.gif[/img] 7 [img]/images/graemlins/heart.gif[/img]

Preflop: MP limps, MP1 limps, Hero completes, BB checks.

Flop: 9 [img]/images/graemlins/diamond.gif[/img] J [img]/images/graemlins/heart.gif[/img] 5 [img]/images/graemlins/club.gif[/img]
Checks all around.

Turn: T [img]/images/graemlins/heart.gif[/img]
Hero bets $4, all three players call.

River: 5 [img]/images/graemlins/heart.gif[/img]
Action?

I was min betting to turn to get a feel for my hand as well as the possibility of a backdoor flush. When all three players just called, I was a bit confused. How do I play this river?