Lets get some terminology correct first in this discussion before continuing.
Juvenile salmonids that are still in the river prior to migration are parr. Smoltification is a transition that takes place in the estuary as fish migrate through it. When completed, they are known as smolt.
The reason behind a hatchery rainbow trout retention opening in July and August is to eliminate juvenile hatchery marked steelhead that are released but do not migrate into the ocean because their release size is too small. Reducing the number of hatchery steelhead from becoming resident trout is a management decision to keep these fish from interfering with other river inhabitants. They can become potential predator of future juvenile salmonids and other resident fish, etc.
That all sounds good if this is done correctly. As Rod has pointed out, excessive killing of both hatchery marked and wild trout have been happening on the Chilliwack River in July and August. If we are to continue this fishery, then there needs to be a better outreach program so participants are well informed before taking part. To make sure participants are more informative, you need to know who they are. In July and August, these are kids coming with parents to the Chilliwack River recreational corridor for the summer holiday, these are teens who come to Cultus Lake with their peers to party, these are city folks who are out for the weekend to enjoy the great outdoor experience. These are people who are probably picking up their fishing gear from Canadian Tire and Walmart, or cannot differentiate between a salmon and a trout, nevermind the differences between a hatchery and a wild fish.
Personally I have no immediate solution for something like this. If this isn't the priority of enforcement in July and August or if ministry staff don't think this is an issue or if there is no money to keep people informed, it'll continue the way it is. I usually add a little write-up on our homepage and the Lower Mainland fishing report so hopefully some actually see the information before they go out for the first time.