From Green Tides to Shared Opportunity: What Comes Next

Climate solutions don’t always start with new technology, sometimes they start with seeing waste differently.

In Puget Sound, excess seaweed fueled by nutrient pollution and climate change is creating real challenges for shellfish growers. In the piece below, we highlight TRFF grantee Puget Sound Restoration Fund’s Sea-Land project, which is turning this growing problem into a practical, cross-sector solution–connecting marine restoration, soil health, and agriculture.

We’re sharing this work to underscore both the potential and the path forward, and to invite funders to consider how strategic investment can help scale solutions that work across land and sea.

Each summer in parts of Puget Sound, thick mats of a bright green seaweed called sea lettuce wash ashore and tangle around shellfish beds. For shellfish growers, the impact is immediate and can be devastating. These “green tides” clog equipment, smother shellfish and add time, labor and cost to already challenging operations. For surrounding communities, they raise broader questions about water quality, nutrient pollution and climate change.

Green tides are not unique to the Pacific Northwest – they are pervasive on almost every coastline around the world and are getting worse due to climate change and human impacts. Within Puget Sound, green tides commonly occur in shallow embayments and on commercial shellfish farms. It’s a problem that isn’t getting better and may be getting worse with evidence that these tides change the water quality in ways that could make green tides more likely.

At Puget Sound Restoration Fund (PSRF), the Sea-Land program began with a simple but urgent goal: help shellfish growers explore different ways of tackling this growing problem. But as the work unfolded, something bigger emerged: a vision for turning excess seaweed from a nuisance into a shared, climate-friendly regional resource.

Project team members worked alongside shellfish farmers and Tribal partners to pilot removal methods and test practical solutions. They explored how nuisance seaweed could be harvested efficiently, stabilized to prevent rapid decay and transported responsibly.

When it comes to removing green tides from shellfish farms, many growers contend with it in different ways. However, manual removal—using your hands—is difficult and takes a long time. The project team saw a 3.5x increase in their harvest rate by using a mechanical pump system. While faster, using a pump system requires larger upfront and operational costs.

Going into the project, collaborators have long recognized that seaweed has served as a natural soil amendment for millennia, enriching coastal farms long before modern fertilizers existed. With that in mind, the next step was to prevent spoilage and prepare the seaweed by drying and mulching it. The team partnered with soil scientists to test the fertilizer on a variety of crops. On crops tested, it had positive effects significantly increasing growth in kale, Swiss chard, shallot, garlic, onion and cucumbers.

What began as mitigation evolved into possibility. The project demonstrated that green tides are not just a waste stream to manage, they may be a bridge between marine and agricultural systems.

This is where the opportunity lies.

Building on Momentum

• Expanding pilots to new bays and farm systems to understand how scalable and adaptable removal efforts can be across Puget Sound.
• Investing in economic modeling to ensure solutions are financially viable for growers and attractive for private and public investment.
• Building a cross-sector nutrient network that connects shellfish farms with farmers, composters and soil innovators–creating a closed-loop system that benefits both water and land.
• Supporting market development for seaweed-based soil products, helping growers test and adopt marine-derived amendments that improve soil health.
• Clarifying policy and regulatory pathways to make responsible harvesting and reuse easier and more predictable.
• Advancing research on blue-to-green carbon pathways, exploring how harvested seaweed could contribute to climate resilience through carbon cycling between marine and terrestrial ecosystems.

By working collaboratively across sectors, the Sea-Land program initiative has laid the groundwork for a more connected system, one where marine challenges become agricultural opportunities, and where local innovation strengthens regional sustainability.

With continued investment and partnership, Puget Sound has the opportunity to lead in demonstrating how environmental stewardship, economic vitality and climate strategy can move forward together.

The question is no longer whether green tides are a problem. The question is how far we’re willing to go to transform them into part of the solution.

For more information, visit https://restorationfund.org/programs/sea-land/