As noted on the Summer 2005-2006 overview, there was a spike in price in Tasmania on Tuesday 7th February 2006.
This incident can be seen in the following image:
Note that, at this time, Basslink was not operational and hence the total demand in Tasmania was supplied entirely by domestic generation sources.
From this chart, it can be seen that, at the time of the spike in price (15:00 to 16:00 market time) production at the Reece hydro plant was being reduced, whilst production at the Cethana hydro station was being increased).
However, it is not immediately apparent, without conducting further analysis exactly what caused the price spike.