James M. O’Neil reports for The Record:

New Jersey’s lakes are suffering from too much of a good thing.

Namely, nutrients.

Phosphorus — vital in limited quantities — leaches into lakes from septic systems. It pours in with storm water. It courses in from fertilized lawns and agricultural land. It’s introduced to the water from geese excrement, and from shoreline soil eroded by waves kicked up by boats.

And when there’s too much phosphorus, bad things happen to lakes.

“Phosphorus drives major productivity of algae and weeds,” said Steve Souza, founder of Princeton Hydro, a company that helps communities manage lakes. “You need enough nutrients to support a healthy lake, but too much leads to the demise in the overall ecology of those lake systems.

“Basically, our lakes need to go on a diet,” Souza said.

The state considers a lake to have too much phosphorus if it measures above .05 milligrams per liter. Of 245 lakes the state tested in recent years, a third exceeded that amount, said Jack Pflaumer, supervisor for water assessments with the Department of Environmental Protection.

The nutrient spurs the growth of invasive weeds such as milfoil, coontail, and water chestnut, which choke some lakes, hamper recreational activity, and therefore threaten property values. The weeds twist around boat propellers and the legs of swimmers.

“I have young kids and lord knows you’d think they were being attacked by monsters when they get tangled in the lake weeds,” said Jessica Murphy, president of the Lake Hopatcong Foundation.

Excess phosphorus also causes algae blooms, which reduce oxygen levels in lake water, posing a threat to fish and other aquatic life. A pound of phosphorus can generate 1,000 pounds of algae.

Most recently, nutrient overloads have caused lake closings because of cyanobacteria blooms, which release toxins into the water that are dangerous to pets and people.

“Pets go into the scum and it coats their fur, and dogs will lick it off. There have been numerous cases of dogs dying after being in intensely impacted waters,” Souza said.

In humans, the toxins can cause ear, throat and gastrointestinal infections.

But an array of lake community organizations, government agencies and university researchers are tackling the nutrient overloads in numerous ways.

At Lake Hopatcong, in Morris and Sussex counties, volunteers inspect boats before they are launched to keep bits of invasive plants out.

At Lake Mohawk in Sparta, the community requires residents to clean out and inspect their septic tanks every three years.

And several years ago the state legislature passed the nation’s most restrictive fertilizer law, limiting the use of phosphorus- and nitrogen-loaded fertilizer.