“When we started out back in 2015, I couldn’t have imagined the scale of the impact we’d have in the fight against single-use plastic,” said Ms Fee.
Announcing its closure on their website, external, the organisation issued a call to governments and industries to “be on the right side of history”.
It pointed to plastic treaty negotiations which took place in Geneva, in August, and were attended by delegates from 183 countries, but collapsed.
Some countries, including the UK, had been pushing for curbs to plastic production in the treaty, but other nations opposed it.
City to Sea’s chief executive, Jane Martin, said: “A rebalancing of power is needed, amplifying voices of those most impacted by single-use plastic pollution rather than those profiting from it”.
She added: “Small, agile charities like City to Sea cannot de-risk this transition for government and business alone.”
Announcing its closure, a spokesperson said the organisation will be working with partners to secure a “long-term legacy” of its programmes and campaigns.