The Lake Gruenau is an alpine moraine reservoir located in the Stubai valley 2300m above sealevel. The 12m deep lake was surveyed with an echo sounder as a reference for an airborne topo-bathymetric LiDAR survey. The location of the reservoir is totally remote and not accessible by car. The whole equipment, the inflatable dinghy “Happy-Cat Ultralight Katamaran” and the echo sounder system GeoSwath Plus Compact had to be carried to the field site.