Cottonwood and its genus are true poplars - "popples" among the loggers - and are all fuzzy with interlocked grain. They grow fast, so there's a lot of space in there for air. Cousins the willows can't be planted near wetlands here, because they use so much water they will "drain" it as surely as a downhill grade. Cottonwoods are nearly as thirsty.
Which is why your nose would quickly realize that the piece you were turning had problems. Stagnant water smells the same whether it's open or contained. When the wood starts to rot, transpiration is blocked, and things get fragrant.
If you have a piece that's consistent and light-colored pretty much throughout you can quickly rough it, and count on it drying nearly anywhere without defect, but with deformity. Tree has a lot of inner tensions from those big branches. Take heart, it will become much more like wood when it's dry, though it will still want proper presentation and a good edge.
Whether it's worth turning is your call. It'll always be soft, will suck finish like it sucked water back when, but it can shine and shimmer pretty nicely if you have the patience. Dough bowls, popcorn bowls, and bark-up types featuring the corky bark are nice.
One final thought. Poplars are good candidates for "cubic rot," which fits your description. The wood dislodges as sharp-edge cubes.
http://www.uoguelph.ca/~gbarron/MISC2003/cubicrot.htm An extreme example, though you can see it in standing dead as well.
