I googled Alberta Petty Trespass Act and got to an article summarizing recent changes to the legislation. (https://auma.ca/news/casual-legal-alberta-strengthens-trespass-legislation). Changes in Feb 2020 include increases to fines and clarifying when a landlord is presumed to prohibit access - i.e. doesn't have to post the land as "No Trespassing".
"The amendments to the Petty Trespass Act also clarify when notice is no longer required to be provided to a trespasser. The list of areas where notice is now essentially presumed, as provided for in the Petty Trespass Act, includes lawns, gardens, land used for the production of crops or raising of animals, lands surrounded by a fence or natural barrier and lands that are enclosed in a manner indicating the owner’s or occupiers’ intention to keep individuals or animals off the land."
So it would seem that where a fence has been set back from the bank, to keep livestock in the field and out of the creek, there is no presumption that the landowner is intending to prohibit access. I'm thinking about Dog Pound upstream of Rge Rd 43 (although I haven't fished that water for several years, so it might have changed since then). Likewise, where a fence is not being actively maintained, is in a condition that would allow livestock to step over the sagging wires and has been like that for a while (I'd say a year at least), there is no presumption of an intent to prohibit access. But all this means nothing if the landowner has posted the land: a sign leaves no room for presumption, it is an express statement of intent, even if the fence hasn't been maintained. Ditto, if a landowner tells you to get/stay off their land, it doesn't matter whether they have posted the land or maintained the fencing. The lack of signage or fencing might give you an excuse for having inadvertently trespassed, but once you are informed of the landlords intent that excuse no longer holds water ... pun intended.