Digging in the creek will keep you out of trouble as long as you fill in every hole you dig, keep it tidy and take your rubbish home.
You have a lot to read about, not every area is the same with rules. Some areas want you to dig in the creek, or have markers out of the creek saying how far you can dig. I keep to what is on my maps, showing where the Crown area of the creek reaches to 20ft to both sides of the current creek shape.
On the youtube vids, they are probably still within the limit of the creek area and where they are still allowed to. There are grey areas everywhere on this subject, but simply, keep it clean, and keep yourself out of trouble. If it seems wrong, then simply don't do it. There are many creeks that have great gold right in them.
If you get out to the golden triangle, you will notice that it is a very different story out there with diggings, but that basic rule of filling in holes should still be stuck to.
You have to work your own way around problems here and there though.
Fill in your holes, and set an example for other prospectors. You can't control other people, but you can control your own actions. I have seen areas completely maggoted by prospectors, but still, a tree falling in the creek or flood would cause much more damage than that damage I have seen. I have filled in many holes that others have left right in the middle of the creek, thanks for that whoever you are 8).
My biggest environmental 'hate' where I live is wombats. They dig and tunnel right under the massive tree roots, causing the tree to fall right over the creek where it is left for years, blocking the creek, forcing the creek to create a new route. And they don't even look for gold under there!! ...hmmm train wombat gold sniffers...