Creative thinking! Similar to the Eco-Auger
http://smartproductinnovations.com/eco-auger/index.php
also a spiral
also fish safe, a good idea
all these are hard to hold in place, however since the axis is parallel to the current, you need a boat or raft to hold it.

Hydrovolts recently won First Prize in the Imagine H2O Water-Energy Nexus business competition. It was a national finalist in the 2009 Cleantech Open and won the CTO’s National Sustainability Award that year. Many more details are available at http://www.hydrovolts.com

– Burt Hamner