CHARLOTTE AMALIE, U.S. Virgin Islands − Over the past few months, high bacteria levels have forced officials to warn swimmers and fishermen to stay away from several beaches in the U.S. Virgin Islands, officials said Monday.

Runoff from passing storms was likely responsible for the bacteria, causing residents' septic tanks to overflow and animal waste from farmland to wash into the sea, said Dean Plaskett, commissioner of the Natural Resources Department.

It usually takes two or three days for the water to clear before the warnings are lifted, Plaskett said.

Authorities issued seven warnings last month for people to avoid 11 beaches in St. Thomas, St. Croix and St. John, said Aaron Hutchins, a spokesman for the U.S. Caribbean territory's Environmental Protection Division. Last week, three beaches were also under advisories, he said.

No warnings were in effect Monday despite heavy morning showers.

The territory's three islands attract millions of tourists each year to its idyllic beaches and azure waters. So far, there have been no reports of illnesses related to the high bacteria levels.

In July, the Natural Resources Department started weekly tests of water quality at 43 beaches.

Discharged waste from sailboats and pollution from large commercial ships may also contribute to the high bacteria levels, Plaskett said.

Boats must be farther than 3 miles (5 kilometers) at sea before they can legally discharge wastewater near the U.S. Virgin Islands. Officials say that many boats violate the law although few are caught.

In St. Croix, malfunctioning wastewater systems sometimes caused untreated sewage to flow frequently into the streets and sea, forcing the temporary closure of several beaches earlier this year. The beaches have since reopened and authorities installed new pumps at sewage plants, reducing the number of wastewater problems on the island.

The U.S. Virgin Islands has a population of about 110,000.

Source: Associated Press