Hi Carol,

It certainly does look like the middle trunk is in trouble. Because of the size of the tree, and it's location along the canal or lake, I would recommend hiring an arborist to give you an honest assessment of the tree. There will be a charge for the visit, so I recommend hiring an arborist who is certified through the International Society of Arboriculture (ISA), as those folks have the best training to assess individual trees. 

You can find a certified arborist at this site:

https://www.treesaregood.org/findanarborist/findanarborist

If no one comes up in the search of the Gladwin area, expand the radius of your search. When a list is generated, pay close attention to the qualifications each person has (on the right side of the page). I would recommend calling someone who has experience with hazard trees, as that person can assess if the tree has the structural integrity to withstand the removal of the middle trunk and continue to survive.

If you have follow up questions, please feel free to respond to this message, or contact me directly using the information below. 

Thank you,

Julie