$5/$10 at Party.

2 limpers and i raise to $50 with [Ac]. LP cold calls and everyone else folds.
I just sat down and have $990 to start after posting a blind a couple hands ago. He has me covered. I have notes on him from lower stakes that basically say hes a bad LAG fish. Ive seen him raise with A7, K7s and call raises with Q8s. Things like that.

The pot is $135. The flop comes [9h][4s]. I bet $90 and he calls.
Pot is $315. The turn is the . I check and he bets $275. I call.
Pot is $865. The river is the . Check or bet?

He's a LAG fish? check. if he doesn't put you in with his river bet, rasie all-in.

He bet the turn because of one or more of these 3:

1) You checked, showing weakness / fear of the flush or set.
2) He has a 9.
3) He has a spade. Maybe 2.

Most LAG's I play with check that turn behind you if they fill up. He most likely doesn't have it.

If you check again and he's LAG, he'll bet the river.

... at least if you were playing NL$25, that's what you should do.

I checked. I really thought he would bet but he checked behind. He had KQ with the . This one cost me because I really doubt he wouldve folded.

not much of a LAG to check that river with the second to nut flush. I think you need to reevaluate your read.

I was definately not folding. I thought if I bet that river after check/calling the turn it would be obvious that I had the . I thought maybe if I checked he would put some kind of bet out there hoping that I didnt have a spade.