when my bait gets into the hydrilla and i pull it up , the hydrilla has a strong smell of Garlic !  is it starting  to rot ? or is it just the heat causeing this ?

Hydrilla generally doesn't have a bad odor.  However Muskgrass does. Garlic smell is pretty much what muskgrass smells like.  To someone who doesn't know any better, it would look like hydrilla.  

But they do have distinct visual difference. 

 

If the hydrilla had been recently sprayed, it may have a chemical odor.  Komeen and diquat dibromide mixes tend to have a distinctive odor.  Take a photo of it next time you are out.

don't know how to put pics on here with android phone, but thanks i will look that grass  up because this is in a reservoir for the county.