The idea of using an aluminium ladder instead of steel is quite a weight saver and more than enough strength. Use high strength bolts, instead of welding, where welds may fracture, bolts wouldn't. There are fibreglass extension ladders, but would the slight weight savings be worth it?
To me , weight saving's being worth it depends on access to the water & availability friend's to help move that dredge into the stream. If your trying to do this by yourself ,then by all means it would be worth it!