They are refering to a lake in the Shalbatana area:

[Shalbatana Vallis is an ancient river valley on Mars, located in the Oxia Palus quadrangle at 7.8° north latitude and 42.1° west longitude. It contains our first definitive evidence of a Martian shoreline. This shoreline was part of an ancient lake 80 square miles in size and 1,500 feet deep. The study carried out with HiRISE images indicates that water formed a 30-mile-long canyon that opened up into a valley, deposited sediment, and created a delta. This delta and others around the basin imply the existence of a large, long-lived lake. Of special interest is evidence that the lake formed after the warm, wet period was thought to have ended.]

From: http://en.wikipedia.org/wiki/Shalbatana_Vallis

I found similar info on other sites (somehow, I'm not surprised).

Interesting.