Garter snakes are difficult to identify to species level. They are highly variable in colour and pattern, and the more specific diagnostic traits, such as the numbers of specific scales, are not always easy to see at the time, or to get a clear photo of. In the area that I have seen them - Vancouver Island - there are 3 species, Thamnophis sirtalis, T. elegans vagrans and T. ordinoides.
I have posted one set of photos so far, seen here, which I identified as a common garter snake, T. sirtalis, an identification that I am rather less sure about now. I have subsequently photographed two more, and I'll attach these at the end of the post. The original I now suspect to be T. ordinoides, and the second T. sirtalis, while the third could be T. elegans vagrans, but realistically all these are little more than guesses.
So, if anyone out there knows what's what with these species, and can give me a better idea of what I'm looking at, I would be immensely grateful. Please ask for larger versions of any photos, or of any from different angles - I can't promise I'll have them, but I'll see what I can do.