For more than two decades, the creators of environmental films and the people who love them have made the annual trek to Washington, D.C., for the Environmental Film Festival. The oldest and largest festival catering to the genre, it will host more than 150 documentaries, guest speakers and Q&A discussions in its 23rd session, which will run March 17-29, 2015.

"We were the original — we tend to show the films first, and other festivals follow," states Helen Strong, public affairs director for the festival, citing such past premieres as "Gasland," "Hot Water" and "Watershed." The 2015 event follows the theme of Climate Connections, and many of the films "will address effects of climate change on the world's natural systems and highlight resilience to the threat of climate change to life on earth," Strong says.

Documentaries booked so far include "Cowspiracy: The Sustainability Secret," which argues that animal agriculture is the most destructive industry on the planet; "Seeds of Time," about the efforts to protect the world's food supply by saving seeds; and "Just Eat It: A Food Waste Story," which confronts the implications of the startling fact that 50 percent of all food is thrown out each year in America.

Wildlife and nature films will be well represented, including "The Leopard in the Land," about snow leopard conservation in Mongolia; "The Penguin Counters," showing how penguins are adapting to climate change in Antarctica; and "Field Biologist," about a young scientist's efforts to save the endangered mangrove hummingbird in Costa Rica. The winners of the 2014 Wildscreen Film Festival in Bristol, England will be on the bill, along with sneak preview screenings of several work-in-progress films.

French director Luc Jacquet, the Oscar-winning director of "March of the Penguins," will present a clip from "The Ice and the Sky," about glaciologist Claude Lorius's study of climate change's effect on the Antarctic. "Watershed" director James Redford will return to the festival with footage of "Happening," about renewable energy solutions. The sneak peek list also includes "The Atlantic," a film about the effect of offshore drilling on marine life and fisherman in Norway and Ireland, and "Dear President Obama," director Jon Bowermaster's appeal to elected officials to stop hydraulic fracking.

In addition to feature and short documentaries, the festival will also screen narrative and children's films with environmental themes, such the animated feature "Adventure Planet," about energy-hogging devices threatening to destroy the Earth.

While the festival remains the centerpiece, Strong says there are many off-season screenings and events throughout the year, and information about those will be posted on the festival website. The full schedule of festival events, which take place at 65 venues across Washington, D.C., and most of which are free, will be available in February.

Related on MNN: