TRUE.
The technical information about the various fields of science is documented through data, maps, graphs and texts. In the case of the depth of large lakes, this technical work is carried out by marine geologists. If you just want to know out of curiosity, maybe you can find it on the internet. But if you need to be sure for a research or technical work, you should consult the technical reports of the area, which are drawn up by university researchers, government etc. These institutions have all the technical apparatus and data that support the results of the research, in this case, the depth of the lakes.