So, you river two pair...

[chaz64]

...bet, and get raised...

Paradise Poker 0.50/1 Hold'em (9 handed) converter (http://www.selachian.com/tools/bisonconverter/hhconverter.cgi)

Preflop: Hero is BB with 3/images/graemlins/club.gif, A/images/graemlins/diamond.gif.
UTG calls, UTG+1 calls, MP1 calls, MP2 calls, <font color="#666666">1 fold</font>, CO calls, <font color="#666666">2 folds</font>, Hero checks.

Flop: (6.50 SB) 9/images/graemlins/club.gif, 3/images/graemlins/spade.gif, K/images/graemlins/club.gif <font color="#0000FF">(6 players)</font>
Hero checks, <font color="#CC3333">UTG bets</font>, UTG+1 calls, MP1 calls, MP2 calls, CO calls, Hero calls.

Turn: (6.25 BB) 5/images/graemlins/diamond.gif <font color="#0000FF">(6 players)</font>
Hero checks, UTG checks, UTG+1 checks, MP1 checks, MP2 checks, CO checks.

River: (6.25 BB) A/images/graemlins/club.gif <font color="#0000FF">(6 players)</font>
<font color="#CC3333">Hero bets</font>, UTG calls, UTG+1 folds, <font color="#CC3333">MP1 raises</font>, MP2 calls, CO folds, Hero...

Three bets, because other players are trapped?

Or calls, because someone may have made a straight or flush?

Comments appreciated.

[einbert]

Just call, MP1 has been check/calling the whole way down so he probably just made a flush. Don't 3-bet this, but do call it down.

[LowDown22]

I would only call. I don't think you're good often enough to 3bet that river.