VOP files contain project data for projects created using VH OTTHYMO, an application for modeling, analyzing, and simulating hydrological phenomena. The application allows users to design and manage storm water drainage ponds projects.

VH OTTHYMO developer offers a 30-day free trial version of their software, which can be used to open VOP files. Full license costs are negotiated individually. Civica offers only a Windows version of VH OTTHYMO.