In Hawaii, there's almost always some kind of volunteer project for visitors to get involved in – for instance, cleaning up public beaches, restoring forest and mountain trails, or pulling invasive exotic plants – even if it's just for an afternoon. To find volunteer opportunities, ask your hotel concierge, check alternative local newspapers and websites like Craigslist (http://honolulu.craigslist.org), or contact nonprofit organizations working on the islands directly, including:

Conservation Connections Browse eco-conscious volunteer gigs and internships on the main islands.

Friends of Haleakalā National Park Sign up for a monthly three-day environmental service trip in Maui's national park.

Habitat for Humanity Help build affordable housing in some of Hawaii's low-income communities.

Hawaiian Islands Humpback Whale National Marine Sanctuary Apply for long-term vounteer opportunities on Maui, Kauaʻi and Oʻahu; annual 'Sanctuary Ocean Count' days are open to all (pre-registration required).

Hawaii State Parks Partners Short- and long-term volunteer opportunities restoring native habitat, trails and historical and cultural sites on all the main islands.

Hawaiʻi Wildlife Fund Day projects and week-long volunteer vacations support turtles and monk seals and marine conservation on Maui.

Kokeʻe Resource Conservation Program Short- and long-term volunteers help eradicate invasive exotic plants ('weed busting') in Kauaʻi's upland forests.

Mauna Kea Visitor Information Station (MKVIS) Volunteer Program Long-term volunteers staff the visitor center and bookstore and assist with public stargazing programs.

Pacific Whale Foundation Organizes land and ocean-based volunteer excursions on Maui, mostly day outings.

Sierra Club of Hawaiʻi Educational volunteer service trips on Maui, Kauaʻi, Molokaʻi and the Big Island are all-inclusive, week-long working vacations for club members. Local island chapters organize half-day and day-long volunteer outings.

Surfrider Foundation Island chapters of this nonprofit organization sponsor family-friendly volunteer days doing coastal cleanup and habitat restoration.

USGS Hawaiian Volcano Observatory Full-time volunteers help monitor the Big Island's volcanoes; minimum three-month commitment, apply in advance.

WWOOF Hawaii World Wide Opportunities on Organic Farms lists short- and long-term opportunities at 300 farms on five islands.