<p>Synthesis of water hyacinth stem (WHS)-based bioadsorbent for the removal of methylene blue (MB) and Congo red (CR) dyes from synthetic wastewater. The characterization and analysis use various techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) before and after adsorption of methylene blue (MB) and Congo red (CR) dyes. The optimum process conditions were found using response surface methodology techniques for both methylene blue MB dye and Congo red dye concentration with the various parameters such as pH, bioadsorbent dose, concentration of dyes, temperature, and stirred speed. The bioadsorption of dyes through batch process and also isotherm and kinetics using WHS-based bioadsorbent. The experimental result found the removal efficiency (&gt; 94%) for methylene blue and (&gt; 90%) for Congo red along with maximum adsorption capacity for MB as 2.89&#xa0;mg/g and 2.48&#xa0;mg/g for CR. The dye removal process was found to be most suitable for Temkin isotherm model (<i>R</i>² = 0.97) with pseudo-second order of kinetic model (<i>R</i>² = 0.99) for both dyes. The water hyacinth-based adsorbent effectively removes both cationic (MB) and anionic (CR) dyes, with removal efficiencies exceeding 94% and 90%, respectively.</p>