No strong reads, villain lost his stack the hand previous to this one with AQ vs AK on a Axxxx board and reloaded.

PokerStars No-Limit Hold'em, $0.25 BB (7 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

Button ($29)
SB ($28.60)
BB ($9.35)
UTG ($8.40)
Hero ($21.50)
MP2 ($17.70)
CO ($25)

Preflop: Hero is MP1 with Q, Q.
1 fold, Hero raises to $1, 1 fold, CO calls $1, 3 folds.

Flop: ($2.35) 5, 6, 6 (2 players)
Hero bets $1.5, CO calls $1.50.

Turn: ($5.35) 4 (2 players)
Hero bets $4, CO calls $4.

River: ($13.35) 8 (2 players)
Hero ???

To me, villain's line reeks of the flush draw so what is your plan on the river here? check/fold?