The Old Town canoe with serial number 188576 is a 16 foot long guide model with a keel. It was built between February, 1972 and March, 1974. The original exterior paint color was dark green. It was shipped on April 19th, 1974 to Minneapolis, Minn. A scan of this build record can be found by following the link at the thumbnail image attached below.
This scan and several hundred thousand more were created with substantial grants from the Wooden Canoe Heritage Association (WCHA) and others as you probably know well. A description of the project to preserve these records is available at http://www.wcha.org/ot_records/ if you want more details. I hope that you will join or renew your membership to the WCHA so that services like this can continue. See http://www.wcha.org/about-the-wcha/ to learn more about the WCHA and http://store.wcha.org/WCHA-New-Membership.html to renew.
It is also possible that you could have another number or manufacturer if this description don't match the canoe. They stopped keeping paper records around 1994 as shown at http://www.wcha.org/catalogs/old-town/oldtown_chart.html so there isn't a build record for number 598819. Sorry,
I don't believe that Old Town has issued serial number 5988819 yet so you may want to check that number again. The page at http://www.wcha.org/catalogs/old-town/models.html says that "Their millionth serial number was issued in 2003" so it will probably take much more than a decade to reach 5,000,000.