Someone said that the road to Hell is paved with good intentions.
The Mottled Duck, Anas fulvigula, is a cousin of the Mallards, but it is adapted to breeding and living in the Southern saltmarshes and does not migrate. It is hard to say just how many remain, and how many of those are 100% Mottled Duck.
Many tame Mallards have been released, and many people have fed migrating Mallards, resulting in a non migrating population of Mallards. Normally, there would be no Mallards here in breeding season, but now the Mottled Duck is slowly being absorbed.
Who knows if the resulting hybrids will be able to succeed in a saltmarsh environment, only time will tell.
Around the pond at the county health center here you will see some strange looking ducks. They are a blend of Mallard, Peking, and Muscovy. they survive well, as long as someone feeds them, but, I doubt they'd last very long at all in a saltmarsh, fending for themselves.