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Beth Hetrick, left , and Amber Johnson, right, both of Manteca, have a water fight in the cool waters of Shadow Cliffs Regional Recreation Area in Pleasanton, Calif., on Monday, June 18, 2012. (Jim Stevens/Staff)

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PLEASANTON -- Swimmers at Shadow Cliffs lake are being advised not to swallow the water because of high bacteria counts, but the reservoir remains open for recreation.

The East Bay Regional Park District said Wednesday that water quality tests at the lake in July found coliform bacteria in concentrations exceeding state health levels, but they were not high enough to trigger a lake closure.

Swimmers at the lake in Shadow Cliffs Regional Recreation Area should refrain from swallowing water. After their outing, swimmers should take a shower and dry off thoroughly, said Emily Hopkins, a park district spokeswoman.

During hot periods in summer, it's not unusual at regional park lakes to have high bacteria readings, she added.

The 80-acre swimming lake at Shadow Cliffs is a former quarry site.

Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff