This paper elaborates a real-time, full-scale, hands-on field experience of jet grouting in river borne materials (RBM). A 316 m long (approx.) earthen dyke of height varying from 6 to 18 m (approx.) was constructed with available river borne material (RMB) on river bed and sides of the river. The key function of this dyke was to isolate the working front in the spillway and plunge pool area from flowing river water just downstream of a rock fill Dam of a hydropower project in India. Sides of dykes was resting on poor geology of riverbanks with highly fractured sheared phyllite rocks. Jet grouting technique was deployed to improve the properties of Dyke constructed with RBM and to reduce the water seepage through dyke body. Analysis of Drilling penetration rates, grouting rate and pressure, cement intake etc. is done across the length of the dyke and along the depth of grout holes. Variation of size and strength with depth of jet grout column could not be tested in field as it could make dyke porous and unstable. Efficacy of jet grouting was proven as it kept the work front practically seepage free for about 3 months even under the varying water depth of 3–12 m along the one side of dyke and river discharge of 100–1200 cumec in non-monsoon season. This experience shall reinforce the confidence of practicing engineers and academician in adopting jet grouting technology in highly variable and porous materials like RBM. Jet grouting methodology, materials, test results, effectiveness, challenges faced, comparison with similar works and scope of further research in detailed in this paper.