## 1 Introduction  
Nuclear power plants (NPPs) and thermal power plants (TPPs) rely on large volumes of cooling water to maintain operational efficiency. This practice, known as thermal discharge, can significantly impact aquatic ecosystems. With the thermal efficiency of coastal NPPs typically around 33%, and supercritical large-scale TPPs achieving efficiencies of up to 40% [1], a significant portion of the energy input is dissipated as waste heat into cooling water. To facilitate efficient cooling, many power plants are strategically located in coastal areas, leveraging vast bodies of water as heat sinks.  
As of July 2023, China operates 17 NPPs with a total installed electrical capacity exceeding 57,000 MW [2]. Each 1000 MW unit discharges approximately 41.4 m\({}^{3}\)/s of cooling water at a temperature increase of around 9.0 \({}^{\circ}\)C [3]. The substantial volume and elevated temperature of this discharge raise concerns about its potential ecological consequences, including altered water temperature regimes, disrupted marine ecosystems, and reduced biodiversity [4; 5; 6; 7; 8; 9; 10; 11; 12].  
Coastal thermal discharges from NPPs can have significant ecological impacts. The construction of intake and outlet structures alters tidal patterns, potentially leading to erosion, sedimentation, and geological instability [13; 14]. Water withdrawal and entrainment can directly harm aquatic organisms [15]. Elevated water temperatures from thermal pollution can disrupt the physical and chemical properties of the water body, affecting aquatic life and ecosystem functions [4; 6; 7; 8; 12; 16; 17]. Additionally, biocides released from cooling systems can contaminate water and harm aquatic organisms [18; 19; 20]. By understanding the complex interactions between thermal discharges and the marine environment, we can develop strategies to minimize environmental impact and ensure sustainable power plant operations.  
To accurately assess the environmental impact of thermal discharge from NPPs, it is essential to delineate the affected area. Field measurements, while providing precise data, are often costly and logistically challenging [21]. Numerical simulations, though useful, can be limited by model assumptions and may not accurately represent real-world conditions [22]. Thermal infrared remote sensing offers a cost-effective and efficient method for monitoring large-scale thermal plume dispersion. It can reveal interannual and seasonal variations in plume patterns [3; 23; 24], influenced by factors like tidal currents, wind speed, water depth, and plant capacity [25; 26; 27; 28; 29; 30; 31].  
This study pioneers the use of long-term Landsat thermal infrared imagery to quantitatively analyze and compare the impacts of thermal discharge with coastal environment regulations. By comparing sea surface temperature (SST) variations between environmental functional zones (EFZs) and a reference region, the study quantifies the incremental SST rise attributable to HYNPP's thermal discharge. The analysis focuses on the following: (1) Annual and seasonal fluctuations in SST increases induced by thermal effluents. (2) Spatial extent and magnitude of HYNPP's thermal influence within each EFZ. It is important to note that this study primarily focuses on surface-level SST variations and does not delve into the vertical temperature profile of the water column.