Crime Scene Evidence

by Richard
(China)

Hello. I am writing a crime novel and there are two questions I want to find answers to:

1. For how long can identifiable DNA or other forensic evidence be extracted from bones once they are immersed in water? For example if a victim is found in a fresh water lake.

2. If blood was deposited on a wooden built boat how long would that last to be able to extract enough information to match the bones in the water?

Grateful for you answers so I can finish my book!

Thanks

Richard