Heavy rains that inundated the Great Lakes region this spring will fuel another massive algae bloom across parts of western Lake Erie later this summer, researchers said Thursday.

Scientists with the National Oceanic and Atmospheric Administration expect this year's bloom to rank among the top five since it began measuring their severity in 2002, according to their annual algae forecast for the lake.

What's not known is how toxic it might be or whether it will pose a threat for cities in Ohio and Michigan that draw their drinking water from the lake.

Algae blooms that produce toxins and can sicken swimmers and harm fish are becoming an increasing concern nationwide, causing water warnings this year from Vermont to the Gulf Coast.

Environmental officials in New Jersey have been telling people to stay out of the state's largest lake since late June and beaches in Mississippi have been closed in recent weeks by a bloom fueled by polluted Midwest floodwaters pouring from the Mississippi River.

Lake Erie, the shallowest and warmest of the Great Lakes, has been hit particularly hard over the past decade. It was five years ago when a toxic bloom caused a two-day shutdown of drinking water in Toledo.

Researchers, using a scale for rating the severity of the bloom, expect it to be a 7.5 this year - short of the most severe outbreaks this past decade but still a significant one.