Tour operators must use their "financial muscle" to make hotels improve swimming-pool safety, the Consumers' Association said following a survey showing 65% of 43 hotels in Cyprus and Gran Canaria have dangerous pools.
Only 10 hotels passed an expert's inspection, with five rated poor and 28 dangerous.
The worst pool was at Tamaran Apartments in Gran Canaria, which allegedly had sudden depth changes and poor depth markings, badly positioned no-diving signs and a diving board which was too high.
Gustaf Dahl, the hotel's manager, denied the pool was unsafe. "The pool has been there for 30 years. There's been no problem," he said.
Eight British children died last summer in hotel pools abroad.