I took a day trip from Milford Central Park to Hudson Mills Rapids with my 15' fiberglass sea kayak and experienced about every condition you can on inland waterways.
Paddling from Milford to Hubbell Dam is easy going as the water is very slow moving. Taking the portage over the dam by myself with a kayak loaded with day trip gear was a little challenging but not impossible. Fully loaded kayaks and canoes will require 2 people to get over this dam. Kayak dollies won't do you any good here because of the steep steps. There's room enough to carry your boat if you'd like.
Paddling on to Kent lake brought 15 mph winds over and open water. There's not too much boat traffic here, but I'd recommend keeping close to the Eastern shore. The East boat launch has restrooms up the hill if nature calls. There's plenty of space for you to leave your boat but be mindful of other people loading their boats into the water. If you're traveling downstream, the boat launch is just around the corner to the left of where the sailboats are docked.
The portage on the south side of Kent lake is about a block from the shore so you'll need to carry your boat or put the kayak on a dolly. The "kayak slide" doesn't really slide so well, but if you have a plastic boat, you're probably OK. I rolled my kayak down to the shore on a dolly and it was a breeze. There's some large rocks when you put your boat back into the water so you need to be careful. There's some concrete weirs that jut out into the water. NOT ALL OF THEM ARE VISIBLE. You'll see some protruding from the shore, but there's a bunch of giant concrete blocks hidden that you can't see. Don't go too fast until you're far away from the dam.
Island Lake Rec Area is beautiful and you can make very good time through the sandy bottom river areas. The water there is reasonably deep and moves quickly. As you progress down the river the road noise from US23 will get louder, you'll know you're getting closer... Between US23 and Huron Meadows Metropark is quite a few downed trees. Take it slow. This is best suited for small boats as I had quite the challenge navigating through the fallen trees. At one point I had to lay flat out to get under a tree that spanned the entire river. There was only one of those points, however, and the other times I wove my way through. This stretch is not for novice kayakers.
Huron Meadows Metropark is not a very kayak friendly stop. The "launch" point is a small sandy section that can barely fit your boat and then you have to go up a steep hill to get up to the picnic area. There are restrooms up the hill and to the right and some nice shade, but you'll need a kayak dolly to get up and down the hill.
From Huron Meadows to Strawberry lake is mostly residential areas. Beware of lots of pontoon and speedboat traffic. On Strawberry lake you cannot see the river exit. Go straight toward the point with the flag pole and follow it around to the right. Stay close to the shore on your left and that'll take you out. There is A LOT of motorboat traffic here so be careful. Make sure other boats can see you, and push hard to get across the lake. The next several connecting lakes are much of the same with lots of boat traffic.
Base Line Lake is the last major lake and it has less motorboat traffic, but be prepared for higher winds. Fortunately, you just go straight across the lake to reach the exit, but if you have a rudder, now is a good time to use it. Between Base Line Lake and the Flook Dam is a restaurant, Riverside Pizza, which has a dock where you can hop out an grab a bite to eat. There will be many pontoons parked there as well so find a safe place to tie your boat off. There's a paddle sports place right next door that is out of business that may have some extra dock space.
Flook Dam is not an easy portage. There's large, wide steps made of wooden beams and gravel or a narrow concrete stairwell. No kayak slide, rollers, or anything. Either way, be prepared to carry your boat up and down a moderately steep hill.
Between Flook dam and the Canoe/Kayak campsite in Hudson Mills is a "rock barrier" with a "portage" supposedly marked out on the Huron River Trail map...I didn't see it...and the rock barrier is not brief. There's a moderately long stretch of rocks along the way that scraped up the bottom of my boat. If you're going downstream this far, check the water conditions. Shallow water here with a fully loaded boat is a problem. If you know where the portage is, please let me know as I must have missed it. Before the rocky sections is a small rapids that I guess would be Class I. Just stay in the middle, go straight, and you'll be fine.
In Hudson Mills there is a clear sign for the Canoe/Kayak campsite with a small landing nearby. I haven't checked out the campsite, but I plan to later. Just downstream of the campsite is the rapids just on the other side of Territorial Road. There's a big, orange warning sign saying that you might drown if you don't use the portage. There is a small portage right after you get under the bridge. I'd recommend staying right under the bridge and you'll see a very beaten up sign with no visible landing, but there is a small ground clearing slightly above the water line. From there you can take the trail to the right up the hill to the road, or you can continue along the portage to the left and you'll bypass the rapids. There's a steep incline getting back down the river so have your buddy with your or make sure you bring your kayak dolly. If you have neither and are carrying your boat, make sure to put some shoes on so you don't slide.
Throughout this trip, with several brief stops, you can average maybe around 3mph. The water level wasn't really high nor really low when I was on the river and the current was noticeable but not rapid. From Milford Central Park to the rapids is about 32 miles.
That's my quick version of the first 1/3 of the Huron River Water Trail. It's the first time I've ventured down this far and I'll try to add more trip reviews as I continue down. I hope my comments here are helpful.
Flat/Sheltered Water, Open Water/Ocean, River/Creek (Up to Class II)
Number of Portages:
Hubbell Dam - portage on the right with small shallow landing before going up steps with rollers on a steep incline. Rollers stop short of the downstream landing.
Kent Lake Dam - portage on the left of the dam but only accessible after about 1 block walk. Follow the tire tread beaten road. There is a kayak slide, but it doesn't slide very well...rocky landing downstream with quick moving water.
Flook Dam - portage on the left side with big steps going up the hill or a narrow concrete stairwell closer to the dam. No slide or rollers here.
Hudson Mills Rapids - portage on the right just after you pass under the bridge. The water is moving fast so be prepared to cut hard right to get to the small portage landing. Once there, follow the trail to the left for about a block. There will be short, steep downhill section where you need to be careful putting in your boat.
Concrete weirs near Kent Lake Dam - not all the concrete blocks are visible and they span a fair distance! Be careful.
Hudson Mills Rapids - fast moving rapids, shallow water, big rocks. Don't go through it unless you have a small plastic kayak.
For these portages, a kayak dolly is recommended.
Lots of downed trees from Island Lake Rec Area to Hudson Meadows Metropark.
Relatively shallow water from Flook Dam to Hudson Mills Rapids with lots of rocks.