This document outlines Bulgaria's Environment Operational Programme (OPE) which aims to improve environmental infrastructure through 3 priority axes. Priority Axis 1 focuses on water and wastewater infrastructure with a budget of 1.28 billion EUR. It involves constructing and upgrading wastewater treatment plants and sewerage networks to comply with EU directives. Priority Axis 2 addresses waste management with a 367 million EUR budget. Priority Axis 3 preserves biodiversity with 103 million EUR. The document describes the project preparation process and common mistakes under Priority Axis 1.