Depends... The biggest hurdle is regaining your strength and range of motion... and it can be slow and totally prohibitive... That said, the closer you get to feeling comfortable in your boat on dry land, the stronger the graft will inevitably be... your biggest concern is going to be putins and takeouts... stay away from the green if you're recovering from a knee injury..

I am not a doctor and I am a notoriously bad patient, so take my advice with a rock of salt, but depending on how you PT, you could probably be back in 4 months

I haven't had an ACL surgery, but I did have a serious tibial plateau fracture after getting hit by a car on my bike. It also resulted in a torn meniscus which was, according to the surgeon "an afterthought" in the procedure compared to what needed to be fixed. I was in the hospital for six days and on crutches for three months and three weeks. I was kayaking two weeks after I got off of crutches, but only on the Sky and I had to have Dufay carry my boat to and from the water for me. Two months later I was back on Robe with no issues, riding bikes on the road and mountain over 150 miles a week, and generally back to normal. I think I had such a fast return to high function because I worked really hard from the moment I came out of surgery. I listened to everything the pt and doc said. I made it a goal to be off of narcotic pain medication within two weeks of surgery, and then no pain medication two weeks after. I went to the gym and worked out on the arm bike and whatever weight machines I could do without putting weight on my leg. I went open water swimming and just didn't kick. I made sure I ate really well and supplemented with vitamin d and calcium. When I started walking and using my leg/knee again, I diligently followed the pt instructions at the gym and at home, and I iced CONSTANTLY. I iced at home, at work, on the way home from the gym, etc. I remember stopping randomly all the time to buy bags of ice so I could immediately get ice on it after some kind of workout. I pretty much focused only, and very intensely, on my leg/knee and getting it back as fast as possible. It wasn't fun, and I relied a lot on my girlfriend and friends to make it all possible. But both my doctor and pt said they had never seen anyone come back that fast from the injury I had.

I know an ACL is a completely different injury, but I am pretty sure you will be walking pretty quickly which means you will be able to do pt pretty much immediately. Focus intently on your pt and ask A TON of questions. Don't assume you are getting all the information you need to know. Make sure you tell your PT exactly what your goals are. Beyond that, make sure your PT knows what whitewater kayaking entails and what kind of whitewater kayaking you intend on doing. Obviously, you shouldn't be running anything where a swim is a risk until you have some legitimate stability in the knee. But, my PT assumed I was talking about a calm float until I explained exactly what kind of kayaking I engaged in. Then, a different timeline came out from him regarding when I could get back into class V.

In terms of physical therapists, I highly recommend Dave Leffman at Pioneer Sports and Physical Therapy. I know he is on sabbatical right now, but he may be returning soon. Otherwise, I would contact his office for a referral. Dave is very sports oriented and will get you back to whatever you want to do as soon as possible. Another good pt I worked with is Emily Eggers, but I think she might be in Bellingham now.

Final word: if you dont bike now, get a bike and ride it for recovery. Biking is the best way to rehab a knee, hands down.

Good luck, I feel your pain.

I live in tacoma. I have been seeing an awesome physical therapist by the name of Amy Moe with Olympic sports and spine. she has been very supportive of me trying to avoid the surgery and go without an ACL, but now after 12 weeks, i have had zero progression in the past month.  if anything i have regressed.  i havent had any dislocations of the knee since the injury day, but i have had a lot of painful "movement" down there, and i am still fcking limping at 12 weeks. fck.
I am going with Doc Jiganti for the surgery with Franciscan health.

i have been skinning/skiing since the injury, and that was not a good idea.  it regressed the recovery a lot.
there will be some days where i am walking perfectly normal and i think to myself, "hell time to push myself a little bit" and then boom some weird movement and i am back to limping for days. 

i have talked with a few people who are ACL deficient, and they are doing fine.  i have also talked with people who have tried to go without to decided over a year later that they really need the ACL to have a high activity level.

all professional athletes, get the surgery and return to sport and a higher level then before. (that's my plan)

ouch! I havent had my knee pop out of place yet but I have had a few instances of light hyper-extension that hurt like hell. Man I hope I dont have to deal with dislocations.