Villain is an unknown.

After preflop, then him going passive and me potting the turn, this is a pretty scary river - what I mean is, anything he called a potsized turn bet with, he's not really jamming this river for value with worse than my hand.

It could just be a desparation bluff, but I'm not sure he really tries that with only a third of a potsized bet behind.

His hand seems really face up, and I'm fairly sure I'm beat.

I can't fold though, can I?

More interestingly, can I fold if we're deep enough that he has say $12-$13 behind on the river?

Poker Stars, $0.05/$0.10 No Limit Hold'em Cash, 6 Players
Poker Tools Powered By Holdem Manager - The Ultimate Poker Software Suite.

BTN: $3.45 (34.5 bb)
SB: $7.16 (71.6 bb)
BB: $11.69 (116.9 bb)
Hero (UTG): $29.49 (294.9 bb)
MP: $13.33 (133.3 bb)
CO: $26.79 (267.9 bb)

Preflop: Hero is UTG with 6 6
Hero raises to $0.30, 3 folds, SB calls $0.25, BB raises to $0.70, Hero calls $0.40, SB calls $0.40

Flop: ($2.10) Q 6 T (3 players)
SB checks, BB bets $1.50, Hero calls $1.50, SB folds

Turn: ($5.10) 9 (2 players)
BB checks, Hero bets $4.90, BB calls $4.90

River: ($14.90) A (2 players)
BB bets $4.59