The phrase "metre depth" refers to the distance or measurement from the top surface of something, like water or soil, to a point that is one meter below it. Full definition
The entrance starts at the southern part at about 20 metres depth leading 36 metres to the 2 narrow exits on the northern side. (dive-the-world.com)
Over the five years it lost the equivalent of 2.5 metres depth of water, with unknown but large uncertainty. (environmentalresearchweb.org)
«Our initial investigations show that the pipes must be located at between 100 and 150 metres depth in order to extract water that is cold enough» says Eidnes. (sciencedaily.com)