Once you get a maximum depth you will have a better idea about the depth topic. With electricity available you can bottom aerate effectively to reduce chance of winter kills. Removing trees from shoreline will be beneficial. Dead tree roots may provide pathways for water seepage out of the pond. If you live there you may want to consider rebuilding the pond or building a new one with a well made clay liner to reduce summer low water levels. Building a new pond is not a lot more expensive than rebuilding an old one depending on how the job is done.
There is a tremendous amount of reading material here about most all pond topics. Look through the Common Pond Q&A Archive Section for starters.
http://forums.pondboss.com/ubbthreads.php?ubb=postlist&Board=22&page=1Find out how to do searches for information and topics on this forum. The google technique noted in the following topic works well for many.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=107697#Post107697 
