The state health department said heavy rains worsened the situation.
TOLEDO (AP) -- Widespread groundwater contamination on a Lake Erie resort island was the likely source of illnesses that sickened hundreds last summer, the state health department said Tuesday.
Several sources, including septic tanks, have tainted South Bass Island's groundwater over a long period, and heavy rains last summer may have worsened the contamination, a health department report said.
The outbreak of gastrointestinal illness sickened about 1,400 island visitors and residents, ending the tourist season early for many businesses.
People who became sick came down with chills, fever, diarrhea and vomiting after visiting the island and surrounding area, which is about halfway between Toledo and Cleveland.
The island sometimes referred to as the "Key West of the Midwest" has a quaint downtown filled with bars, restaurants and souvenir shops alongside a leafy city park. Thousands come by boat every weekend.
While most vacation homes and businesses that cater to tourists draw their drinking water from the municipal system, about 400 use groundwater from wells for drinking and bathing.
The groundwater collects under the island's surface in cracks in layers of limestone. It's replenished by rainwater and connects to Lake Erie.
But the island's porous soil makes it easier for contaminants such as bird droppings and motor oil to wash into the bedrock especially during heavy rains, the report said. Rising and falling lake levels also could have washed pollutants into the groundwater.
The health department tested 79 wells throughout the island last September. About eight of 10 tested positive for the bacteria coliform, which could signal the presence of other harmful bacteria, according to the report. Three in 10 wells tested positive for E. coli.
The depth of the wells also contributed, the report noted. Many wells were dug 25 feet down, the minimum required by state regulations. Deeper wells draw water farther from potential sources of contamination.
Island leaders already have taken a number of steps to ensure plenty of clean water will be available to businesses and homes with private wells.
The village of Put-in-Bay plans to increase capacity of its water system for this year's tourist season and supply water to some businesses not served by the water system.
Homeowners will be able to haul water to use for drinking, and a new water line will be installed to an island winery.