>What are the major rivers in NK?
The longest river of North Korea is the Yalu, in Korean called the Amnok. It rises on the southern slope of Mount Paektu and flows southwestward for some 500 miles (800 km) to its mouth on Korea Bay. The Tumen (Tuman) River also begins at Mount Paektu but runs northeastward for about 325 miles (520 km) to the East Sea. There are no large streams along the east coast except for the Tumen River, and all the significant rivers, such as the Yalu, Ch’ŏngch’ŏn, Taedong, Chaeryŏng, and Yesŏng, drain to the Yellow Sea. The relatively large valley plains of the western rivers are major agricultural regions.
https://www.britannica.com/place/North-Korea
>Are any of those around major shipping ports or trade installations?
Yes
> Any specific rivers that would allow large ships to pass through to a certain point?
Yes
>Any Evergreen Shipping in the vicinity?
No
Port of Nampo along the Taedong River seems to be the most active. Taedong River doe reach quite a way into the country, but I'm not seeing any vessel traffic north on Kangam. Lack of AIS transmitters maybe? Most vessels seem to be smaller bulk carrier types, figure no bigger than 300 feet long
Hanseatic Unity Chartering, Maersk, and CMA CGM are far more worth watching than Evergreen. There are two smaller outfits I'm keeping an eye on and after months of watching Evergreen ships I'd have to say it'd be nice if they learned how to steer