Freshwater ecosystems harbor an astonishing proportion of the Earth's biodiversity, yet one in four freshwater species is threatened with extinction. One of the most effective strategies for conserving rivers and lakes is the establishment of Protected Areas (PAs). In 2022, countries at the UN committed to expanding PA coverage from 17% to 30% of the Earth’s surface by 2030—an initiative known as the "30 by 30" target. However, traditional PAs have often fallen short in addressing freshwater conservation challenges. Therefore, future PA expansion must specifically integrate freshwater biodiversity conservation needs. In this study, we present an optimized scenario where global PA networks are expanded to maximize protection for freshwater biodiversity while adhering to a 30% area constraint. By leveraging AI-guided optimization algorithms, our approach can strategically allocate protection for all mapped freshwater fish species (13,000 species) across 190,000 river basins worldwide. Recognizing that a purely global strategy may impose uneven conservation responsibilities on different countries, we introduce two complementary approaches. These approaches aim to maximize biodiversity protection while ensuring that PA expansion is equitably distributed at both national and river-basin scales. Our findings demonstrate the significant potential for enhancing freshwater biodiversity protection by strategically designating new PAs. By creating interconnected conservation networks, our approach ensures that species have access to minimum viable protected ranges, ultimately improving their long-term survival prospects.