Has anyone else ever wondered why Riften needs a dock?

Because it's only just hit me that Lake Honrich, goes nowhere, not anywhere that would make having a boat an advantage atleast.

I assume that in lore it is linked to another waterway?

Perhaps because you can fish on the lake? I don't know. hey have a fishery there, so I assume they can fish on the lake? (or they used to)

I thought I recall some NPC stating that it used to be involved in trading as well because I scratched my head at the same thought as well.

Fishing.

I thought there was a river going from there somewhere? Because it seemed like I wondered the same thing myself and that was the only logical explanation.

Ah... yes:

http://www.uesp.net/wiki/Skyrim:Lake_Honrich

The Treva River flows from there to Lake Geir at Ivarstead, which connects it to another river flowing out of Lake Geir and I don't know where that one goes.

Same! Hence this thread. ^^

Yeah I guess that could cover it, but in all fairness, I can fish 10x better with my bare hands. (Really wish a fishing mod would come along soon probably hard though.)

Now, I know "TES Lore" is separate from "TES Gameplay", which is why I wondered if in the "lore" version of Tamriel, there is indeed a connecting waterway.
Otherwise, that NPC who mentions Riften being "The hub of trading" is totally a liar, or on some seriously high dose of skooma. (I am aware that it "used" to be a hub, and that in recent times it has fell into the hands of corruption, but that can't explain how travelling across water to Morrowind was possible. (Pretty sure I heard someone say merchants would come by boat to Riften from Morrowind, maybe wrong)

I looked that route up too, but when I looked at some of the waterfalls along that route ingame, well, I doubt a rowboat would make it, let alone a merchant ship!

Fishing and trade up and down the lakes of the Rift. Represented in-game by the fishery and the dock at the Goldenglow Estate.
And don't forget that the gameworld is only a scaled-down model.

As for being a trading hub, Riften sat on a crossroads between Skyrim, Morrowind and Cyrodiil.

Yeah I get that, "TES Lore" and "TES Gameplay" ;P

Erm, so what about the NPC's who seem to believe it was once a hub of merhcant traders?

E: I see your edit. I am almost positive that the NPC's claimed that it was boats bringing goods from Cyrodiil and Morrowind. Going to check what the NPC's say exactly to lessen the confusion going on in my head right now. xD

http://www.imperial-library.info/content/crossed-daggers only talks about trade caravans to and from Morrowind
I find it unlikely there'd be a river through the Velothi mountains personally. Still, the geography is only an approximation. Just like in Cyrodiil Leyawiin doesn't really block the Niben

It would not be the first example of there being unnavigable waters on Nirn - check out lore vs game for Oblivion as well. For the sake of argument assume fishing. It's entirely reasonable they would have a dock for that.

Ahh, well, I think I have mixed a few different things up in my head.

I'll just go zero-sum now.

If you swim around the Riften Docks, you will know why there are fishing boats on the lake.