Even if the canal were closed, it is a just a matter of time until someone with an evil bent or an adolescent sense of humor deliberately introduces a few carp into the lake -- that's all that's needed.
To those who still claim that humans are far too small to effect the environment, the Great Lakes are a great counterexample. Three times in my lifetime I've watched the biological ecosystem of these lakes change dramatically. The 70s Alewife invasions made hundreds of miles of beaches unbearable, the zebra mussels cleared the water but gave small fish no place to hide and allowed sunlight through to cause the huge blue-green algae blooms that shutdown Toledo's water supply this summer. The Asian carp carp invasion of the Great Lakes is a foregone conclusion. Their DNA is already in Lake Michigan and more exotic species such as the Yangzee river freshwater jellyfish are already found in tiny isolated inland lakes in the Wisconsin north woords. There isn't enough law enforcement to check all of the jet skis, kayaks, ski-boats, sailboats, fishing boats and prevent deliberate introduction. It's already too late, sustainability is impossible. Resilience and/or recovery are our only options.