KM3NeT is constructing two large volume water Cherenkov detectors in the Mediterranean Sea. By instrumenting the water with photo-multipliers, neutrinos can be detected through the Cherenkov light from charged products of their interactions. The dominating signal, however, comes from muons created in extensive air-showers resulting from cosmic ray interactions in the top of the atmosphere. Despite the water column above, the highest-energy muons (>TeV) reach the detectors. Air-showers develop in a non-isotropic atmosphere where the vertical temperature profile, and thus the density, varies over time. The changing density of the atmosphere affects the balance between interaction and decay (to muons) of mesons in the air-showers. Therefore, the muon flux is expected to correlate with the seasons and short-term temperature fluctuations, as confirmed by other experiments. In this contribution, we present a first measurement of the correlation of the detected muon rate with the effective atmospheric temperature (weighted by muon production spectrum and detector response) for the KM3NeT ORCA telescope. The measured rate is compared with simulations, which model the time-dependent detector efficiency and environmental factors for a constant atmospheric
muon flux.