From Garmin: 

Out of an abundance of caution, Garmin has voluntarily chosen to globally recall its 2009 version of BlueChart g2 and g2 Vision data cards. In certain waters, there are inaccuracies and/or omissions in the way that this specific version of charting represents depth contours and depth areas, resulting in the depiction of water depth as deeper than the actual depth under certain display conditions.

Read the whole article here.