ColinChapman
Longtime RPG Freelancer/Designer
Maybe?
Sorry, but when it comes to maps I am a visual guy, so I need to see it to be sure. When I make maps usually there are multiple versions before I settle on something as I experiment with what works (and looks good).
Your description sounds generally OK, but if we look at the real world you have the order of the lakes wrong. Small streams go to small lakes into medium rivers and then large lakes into large rivers into the ocean. So, the question would be why does a large lake drain into a smaller one? How does that smaller one not overflow when there is so much water to flow into it?
Part of your answer is all of the marshy ground, but marshy ground is usually found at the inflow of a river into a lake, not the outflow. Not to say it never happens, but marshes at the entry to a lake is common because there is an elevation change that is allowing the water to pool, rather than continuing to run in a river. When a river leaves a lake, it is generally not marshy because again there is a change in elevation that is causing the water to flow down to the next level closest to the sea (or perhaps even to the sea).
Basically, water is always seeking equilibrium, which is generally "sea level" however that is determined.
Hope that helps more.
That does help, thanks. In my next update, I'll revise the lakes/marshes as I add the rivers.