Millions of cartons of Horizon organic milk contain an oily substance made up of industrially grown algae, the Washington Post reports.

The DHA algal oil made with this algae is marketed as a nutritional enhancement due to its richness in omega-3 fatty acids and is added to Horizon’s DHA Omega-3 organic milk. The Schizochytrium algae used to produce it can replicate between five and nine times a day when fed corn syrup, as opposed to typical algae that replicate just once a day.

“The oil allows Horizon to advertise health benefits and charge a higher price,” writes the Post.

Organic milk naturally contains more omega-3 fatty acids than conventional milk due to regulations requiring cattle to be fed grass rather than grain; the addition of the algal oil artificially boosts these omega-3s.

Some industry experts do not believe that such a product should be allowed to be labeled as organic.

“When an organic milk carton says it has higher levels of beneficial nutrients, like omega-3 fats, consumers want that to be the result of good farming practices … not from additives made in a factory,” Charlotte Vallaeys, a senior policy analyst, at Consumer Reports, told the Post.

The oil's presence in organic milk is due to a 2012 misreading of federal regulations on the part of the USDA, something that the Post reports the agency "quietly acknowledged" but has yet to address with a final rule.

The USDA “maintained the status quo – allowing the use of algal oil, among other things – in order not to ‘disrupt’ the market,” the Post writes.

Horizon milk with DHA algal oil is usually sold at 30 cents more than plain Horizon milk. According to Horizon, 26 million gallons of DHA algal oil milk were sold last year, representing 14 percent of all organic milk gallons sold.

Other milk brands, such as Costco’s Kirkland brand, also supplement their organic milk omega-3 levels with similar additives, such as refined fish oil. Costco sources its milk from Aurora Organic Dairy, which, the Post reported in May, was failing to graze its cattle as required by organic law. This lack of grazing was reflected in the lower omega-3 levels of the milk as compared to other organic brands.

Related on Organic Authority

Organic Valley Seeks to Make Organic Milk More Affordable

Organic Milk and Egg Producers Accused of 'Factory Farm' Conditions that Violate Organic Law

Organic Milk Notably Healthier than Conventional, Study Finds