I caught about twenty chests one day on the misty shore from the floating wreckage. They contained around 15 mid-30 level green items. I went back to do it again and could not find any floating wreckage to fish. This is just north of Dalaran.

the best things i have found fishing and good money makers is in zangarmarsh, goldenscale vendorfish sell for 6g which is a nice sale but i also came across a few broken engine parts that vendor for 10g. a couple hours of fishing the debris in serpant lake and i had almost 100g and a ton of fel iron ore and scrolls(also a lot of fish). with the fish tracker ability it makes it real easy to find the debris. good times