The presence of fluid in the kidneys is mostly due to congenital anatomical factors, or the formation of acquired obstruction factors, you need to go to the hospital for further examination to make it clear: 1, congenital anomalies, such as congenital stenosis of the ureteropelvic junction, or the presence of duplicate kidneys, duplicate ureter, can lead to the obstruction of urine discharge produced by the kidneys, and gradually appear hydronephrosis, congenital anomalies do not have any symptoms in the early stage, and only when they reach a certain level will there be symptoms such as back pain, lumbar distress or edema. The congenital deformity does not have any symptom in the early stage, only when the accumulation of water reaches a certain level, there will be symptoms such as lumbar pain, lumbar sleepiness or edema, which can only be detected by physical examination, and it is necessary to carry out surgery to lift the congenital obstruction and correct the congenital deformity in order to cure the renal hydronephrosis. 2. Acquired diseases lead to obstruction of the urinary tract, such as ureteral stones, kidney stones, ureteral tumors, renal tumors and so on, all of them can lead to the pressure on kidneys or ureters, and urine produced by kidneys can gradually be formed when drainage of kidney is obstructed. Urine produced by the kidney will gradually form hydronephrosis when its discharge is blocked. Acute obstruction, such as that caused by stones, can produce obvious symptoms of low back pain, but chronic obstruction caused by tumors has no obvious symptoms in the early stage, and only when the tumors increase to a certain extent can painful symptoms appear, which can be detected by physical examination at that time.