Summer’s here, and our lakes and ponds are in full bloom again.

What’s “blooming” is the latest crop of cyanobacteria, aka “blue-green algae.” Cyanobacteria are among the most ancient organisms on earth.

They’re a natural component of our aquatic ecosystem. Over eons they’ve become responsive to hot weather and calm water, which facilitate their growth. Weather didn’t actually cause the current blooms, though. The problem arises when certain nutrients, primarily nitrogen and phosphorus, accumulate in unnaturally high concentrations in bodies of water. Gorging on essentially limitless food, algae undergo a population explosion.

Overabundant blue-greens can damage other life forms with which they share the waters. The algae contain natural toxins; killing them off with algaecides releases the toxins intact (though the algae themselves grow right back, within days or weeks). This alone can cause fish die-offs. When the algae die of old age, they sink to the bottom of the pond, absorbing oxygen and creating an “anoxic” environment. Water-breathers suffocate.

The contaminated water also harms non-aquatic organisms, including pets and people, possibly water-birds like ducks and herons. Humans should avoid direct contact with the water.

We can still eat fish drawn from algal waters. Taking care to avoid puncturing internal organs, skin must be washed and peeled away, and the underlying flesh carefully filleted from the bones.

Once these algae bloom, we just have to wait it out.

A toxic lake is useless for recreation, no longer serving as an income driver for local economies.

While in a sense this phenomenon is “natural,” and becoming “normal,” it signals one unanticipated consequence of widespread environmental manipulation. Our primary source of nitrogen and phosphorus contamination is agricultural and domestic fertilizers.

Freshwater lakes aren’t the only fertilizer casualties. When fertilizer run-off enters private wells and municipal drinking water systems, it can trigger birth defects, blood disorders, ovarian cancer, and thyroid problems. In the heart of Corn Country, Des Moines is embroiled in a public battle between the city’s water utility and Iowa’s Big-Ag-dependent politicians over this very issue.

When fertilizer run-off washes down the Mississippi to the Gulf, it fuels a huge annual dead zone, threatening a fishing industry that’s among America’s most productive.

The Chesapeake Bay, continental America’s most fertile estuary, hosts its own massive bloom every year. If the resultant dead zones could be cleaned up, it would increase fishery productivity, tourism, and property values to the tune of $22 billion per year.

Since curative treatment isn’t feasible once the bloom begins, the only remedy is reducing fertilizer run-off. That would take a local effort — it’s local agriculture that feeds fertilizer into Kansas lakes and wells. It would have to be a cooperative and consensual effort; hold-outs would perpetuate the problem.

Farmers commonly employ a two-crop system, alternating corn and soybeans, applying large amounts of fertilizer, and creating bare ground between seasons. Corn plants absorb 50 percent or less of the nitrogen applied in the spring. After harvest, with no plants to absorb the excess nitrogen, it leaches into streams, and from thence into the Bay.

Enough washes away to leave the soil in need of fresh fertilizer before the next planting.

As climate change progresses, we’ll see greater oscillations between extremes — very dry periods alternating with very wet ones. During dry seasons, plant growth is hampered, leaving more unabsorbed nitrogen in the soil. When it rains, it pours, and excess nitrogen residue surges into streams and rivers.

Nationwide, these practices spark higher rates of erosion, and agricultural nitrogen pollution costs about $157 billion annually in damages to the environment and human health.

When many crops have come to depend on synthetic fertilizers to maximize their yields, reducing fertilizer use is a hard sell.

Fortunately, it’s not the only choice.

One of two states primarily responsible for feeding water into the Chesapeake Bay system, Maryland has developed a different approach.

They pay farmers to plant a crop that’s not necessarily even intended for harvest. At $90 an acre, it costs around $22,500 to modify a typical corn operation. That totaled $24 million in Maryland taxpayer dollars in 2015.

As one example, winter-hardy rye is planted right after corn harvest. It absorbs the excess nitrogen before being harvested in the spring to make room for corn or soy, even before it ripens into a grain crop. (Or, as is the case with other cover crops like red clover, it can serve as a “green manure,” tilled under to enrich the soil.)

Chaff can be left “as is;” when farmers plant into it, the dead vegetation helps crowd out weeds and retain moisture.

A 1998 University of Maryland study demonstrated that planting rye after corn reduced nitrate leaching by about 80 percent. When cover crops were used for seven straight seasons, nitrate levels in the water table dropped by more than 50 percent. Proof of concept.

Pay-offs also include higher yields, less erosion, and dramatically less fertilizer use, while preserving or enhancing per-acre profits.

Currently the government pays billions to subsidize a farming practice that’s producing serious adverse effects. Investing a tenth as much in an incentive program — basically hiring farmers as private contractors, not giving them “hand-outs” - to reduce fertilizer run-off could save billions “downstream.”

As well as they have served us, current methods of ag-land management are becoming unsustainable. We can tweak them for relatively little, and harvest the pay-off for decades.

Jon Hauxwell, MD, is a retired family physician who grew up in Stockton and lives outside Hays.

hauxwell@ruraltel.net