The Duke of Cambridge, who is on a short official four-day tour of Kuwait and Oman in the Middle East, joined litter pickers on a beach in Kuwait.
Speaking to the group of environmental volunteers at a nature reserve outside of Kuwait City, William said:
"I hate plastic bottles now and I look at them and I literally think it's the enemy.
"Things are changing quickly but they need to change quicker."
Prince William also said: "We recycle as much as we can at home, but I worry about the chain - where it goes when it leaves us."
The prince also suggested there needed to be a worldwide litter-picking day.
He told the volunteers: "We all need to shift our mindset and you guys are part of the solution."
Before meeting with the litter pickers the prince was shown the rest of the reserve which has 300 species of birds, including greater spotted eagles and flamingos.
He arrived in the country on Sunday and will also attend a celebration marking the 120th anniversary of the 1899 Treaty of Friendship signed between the UK and Kuwait.