PORTLAND, Ore. -- Avoid the Willamette River this weekend.

City officials have issued an advisory against any recreational activity in the Willamette River, one day after a major thunderstorm pummeled Northwest Oregon.

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The storm dumped up more than a half-inch of rain in some areas from Salem to Portland between 3 p.m. Thursday and midnight Friday, meteorologists said. The rain overwhelmed the city's sewer system and sent a mix of storm runoff and raw sewage into the Willamette.

Environmental Services warned people to avoid river recreation -- water skiing, jet skiing, swimming or any activity in which water could be swallowed -- for at least 48 hours after the rains stopped.

Health experts said those fishing from the Willamette should wash their hands thoroughly afterward using non-river water. The fish should be cooked thoroughly to kill bacteria.