Gday Daryl,
This one's been discussed a fair bit in the past, and like it or not that's the restrictions Wide Bay Water have decided to implement in the interest of controlling Water Quality (there primary objective I believe).
Old tech 2 strokes up to 6hp, or 4-Stroke and Direct Injection 2-Stroke engines up to 60hp. This equates to all 2 & 3 Star OEDA (Outboard Engine Distributors Association) rated engines.
Full details are at http://www.widebaywater.qld.gov.au/r...enthalldam.php
Personally, I cannot use my current Bass/Barra boat at Lenthalls either, however thats one of the primary reasons I have my electric only boat. If you get the chance to fish there you might see why it's worth the effort I would hope
Lenthalls is not a particularly large dam and doesn't take a lot to get around, even in a kayak/canoe.
Cheers
Tony