  We use the non-observation of strong lensing of gravitational waves (GWs) in
the first three observation runs of LIGO-Virgo detectors to constrain the
fraction of dark matter in the form of compact objects in the mass range
$10^{6}-10^{9}~{\mathrm{M}_\odot}$. Using a Bayesian formalism supplemented by
astrophysical simulations of strong lensing of GWs, we constrain the compact
dark matter fraction to $\lesssim 0.4-0.6$ with currently available data and
show that they may get significantly tighter in the future. We find that
multiple lensing -- i.e., GWs getting deflected by multiple compact objects on
their way to us -- is possible. By ignoring this, we underestimate the
constraints by a few percent.
