I did my homework and having read this thread on the Devoke Water - Birkby fell BW, thought I'd give it a whirl at the weekend.
The section along Devoke Water is OK, but from Birkby fell to the double walled section above Dyke is mental. Both me and my mate went in up to our thighs in the tussocky bog.
Chatting to some locals the day after I was informed that a horse had drowned there.
If you want a KOM and you have suitable underwater breathing equipment, go for it. http://www.strava.com/segments/5083651