Hey MapleNeil,
I thought the same as you, and generally, you are correct - if you stay in/on the water you are fine. The old, pre-Harper definition of navigable water was any water that could carry a canoe. Most water like this is public access. I would say your creek is 'navigable'. (I'm also NOT a lawyer)
There are exceptions, however, so it is always best to ask for permission.
I found this out the 'hard' way - I was walking down a creek and got caught on a farmers' property. I had to leave the water to get around so I spoke to the owner to get permission to cross his property to another part of the creek.
He informed me that he, and other landowners downstream had title to the whole creek, including the bed, on their property. It was given by some long dead king but still had legal backing (he has had interactions with the local conservation authority and has come out on top). If the property is on a property like his, you would be trespassing if you are on the creek without permission.
He was great, and gave me permission to continue, and outlined how far down people had this exceptional ownership. Not wanting to face a couple big dogs downstream on one of the properties I skipped that bit and got back to the 'navigable' section of the creek.
It seems like this exception is limited to land initially granted to Loyalists after the War of Independence to the Victorian area, unless that land was also a part of Treaty deals with First Nations. On the creek I was on it is public access above a certain line because it is navigable, then private thanks to these title grants, then public below thanks to a treaty signed to protect First Nations fishing rights.