We have stayed at Mew Lake several times but not recently. The bike trail does go past the campground and is a pleasant ride to Rock Lake Campground. The trail is mostly flat and you never know what wildlife you may see along the way. Take a picnic and enjoy a leisurely ride.
Yes, the dump station is down the highway. My memory is not as good as it used to be, but I am thinking about 4 miles to the East on Hwy. 60. It used to be you could not fill up with water at the c.g. but I think that has changed and there may be a couple of spigots you can use. There is not water at every site in any provincial park - just a tap or two around each camping loop. Years ago they put contraptions on that would not allow you to connect a hose - hence the need to go to the fill up at the dump station.
The first 2 weeks of August will be prime time so you will want to make your reservations as soon as they open for the year. We don't stay at a lot of provincial parks so I am not sure when reservations open - that info is probably on the website - but DO IT ASAP. Another c.g. choice to consider is Lake of Two Rivers which is almost next door to Mew Lake. The bike trail is also accessible there.
Hope it all works out for you.
