The former world number one voiced his fears for anyone straying off the fairway after the first practice round on the course.
And Woods is bracing himself for the challenge of adding to his 15 major titles when he takes on his favourite championship this weekend.
"It's just that you can't get out of it," he said of the course conditions.
"The bottom six inches is so lush.
"The wispy stuff, we've always faced that at every British Open. But that bottom six inches, in some places it's almost unplayable. I've never seen the rough this high or thick and dense."
Woods' fellow American Keegan Bradley, the 2011 USPGA champion, added: "I tried not to hit any out of the rough today but I will for the rest of the week.
"It's very spotty. One foot to the left, you are hitting in to the green; another foot and you are chipping out to the fairway. It's a flip of the coin whether you're going to get a good lie or not."
Woods is still a fan of the course, though, saying: "Lytham is certainly up there. I like the layout. It's fair. They don't have to trick it up. They don't have to do anything with it. They can play it as the members play it and it would still be difficult. It's not that long.
"If it's calm, we can shoot some good scores.
"If it's wet, lush, you've got to be more aggressive. Have to see how it's playing. Some years it's fast and some it's not. The two years I played it was quick. The ball was travelling quite a bit. They've made a few changes in tee boxes, lengthened a few holes but most of the bunker adjustments were made the last time."
The 36-year-old's last major win was at the 2008 US Open, leaving him four behind the record tally of Jack Nicklaus.
The Open starts on Thursday.