Wastewater from clothes washing machines are a tremendous low-hanging fruit-type opportunity for addressing the issue.
Eventually, filters built to handle sub 5mm particles will hopefully be built into every washing machine system. Until that filter is developed, however, more plastic finds its way to the oceans daily.
I want to spend the time to develop a simple alternative. A basin that filters water through evaporation. It's a process used successfully to filter water for drinking. Though an interim solution, all I'm proposing is combining tried and true technology to solve a dangerous-but-completely-preventable problem.