The reason? An invasive species called Asian Carp. You might already be familiar with this particular fish (or maybe not). Regardless, the National Park Service has compiled a great overview about the Asian Carp and its impacts.
Lock and Dam No.1 is the last line of defense for the Mississippi River north of Minneapolis where the Asian Carp has not yet established itself as well as an abundance of Minnesota lakes and rivers. We encourage all paddlers and boaters to join us and our partners in the boycott of Lock and Dam system in the Twin Cities. Together we can protect this important resource we all enjoy so much!
For further involvement, check out http://stopcarp.org/ to join the fight to close Lock and Dam No.1 for good!