The 2017 World Hydrography Day (WHD) is observed on which date ?

The World Hydrography Day (WHD) is observed every year on June 21 to publicise the work of hydrographers and to create awareness about hydrography which is an essential science before undertaking any activity on or under the sea. The 2017 theme is “Mapping our seas, oceans and waterways – more important than ever”.