We present observations of two strong-lensing galaxy clusters located within the 90 per cent credible sky localization maps released following LIGO-Virgo ’ s discovery of the binary black hole ( BH-BH ) gravitational wave ( GW ) source GW170814 . Our objectives were ( 1 ) to search for candidate electromagnetic ( EM ) counterparts to GW170814 under the hypothesis that it was strongly-lensed , and thus more distant and less massive than inferred by LIGO-Virgo , and ( 2 ) to demonstrate the feasibility of rapid target of opportunity observations to search for faint lensed transient point sources in crowded cluster cores located within GW sky localizations . Commencing 20 hours after discovery , and continuing over 12 nights , we observed Abell 3084 ( z = 0.22 ) and SMACS J0304.3 - 4401 ( z = 0.46 ) with GMOS on the Gemini-South telescope , and Abell 3084 with MUSE on ESO ’ s Very Large Telescope . We detect no candidate EM counterparts in these data . Calibration of our photometric analysis methods using simulations yield 5 \sigma detection limits for transients in difference images of the cores of these clusters of i = 25 . This is the most sensitive photometric search to date for counterparts to GW sources , and rules out the possibility that GW170814 was lensed by these clusters with a kilonova-like EM counterpart . Based on the detector frame masses of the compact objects , and assuming that at least one Neutron Star ( NS ) is required in the merging system to produce a kilonova-like counterpart , implies that GW170814 was neither a NS-NS nor NS-BH merger at z > 8 lensed by either of these clusters . Also , in the first ever emission line search for counterparts to GW sources , we detected no lines down to a 5 \sigma detection limit of 5 \times 10 ^ { -17 } { erg s ^ { -1 } cm ^ { -2 } } .