I participate with a group that does weekly water testing on Merrymeeting Lake. The samples and results are sent to the UNH Extension Service. A quick search shows that the same is done on Winnipesaukee, in multiple locations.
http://cfb.unh.edu/programs/LLMP/nhllmp.htm
http://winnipesaukeegateway.org/moni.../introduction/
I did not find any of the 2012 water quality reports for Winni. The Merrymeeting one can be found here.
http://www.mmlake.org/MMLA_documents...2%20Report.pdf
The good news is that we have been getting pH readings of 7.1-7.3 all year, consistent with other years. As much of this water flows into Alton Bay, I would expect this to be true in that area also.
While many other factors need to be considered when assessing these numbers (buffering capacity, sample depths/areas/locations, etc), the numbers indicate that acidity of our water is not an issue...yet.