For precise echo-sounding or for research of the boundary conditions of fishing shoal by the ultrasonic echo-sounder, it is necessary to obtain the true shape of the sea bottom from its record. We noted already that when we use an echo-sounder which transmits only ultrasonic waves with broad beam, it is very difficult to obtain a true shape of the sloped and undulate bottoms by the cause of the sounding error. However, if we use ultrasonics of 15 to 3cm in wave length which are now popularily applied, both the transducer and other apparatuses become big and heavy, and they are not suitable to be mounted on a small craft for survey of shallow sea waters, lakes or swamps. It is necessary, consequently, to use a high frequency ultrasonic wave, and we can obtain easily transducer with sharp directivity which can be used in small crafts. In this work, we used ultrasound of 200 to 400kc transmitted from a Barium-Titanate transducer. The experiment was aimed at a cross section of the under-water-valley in an artificial lake of a power plant, to compare the shape of the section surveyed by the triangulation before the lake was filled with water, with that obtained by the echo-sounding method after the water was filled. We have also described some data obtained at field application of newest 200kc echosounder. From the surveyed data, we have obtained the following conclusions. 1) To make sharp beam angle of transducer, it is favourable to apply ultrasound of 200 to 400kc, consequently the transducer becomes compact and the echosounding is easy at a shallow sea waters, lake or swamps, even by a small craft, as the mounting of the sounding apparatuses can be simplified. 2) It is possible not only to obtain true shape of the sea bottom but also to detect even the fish school swimming quite near the fishing shoal by an echosounder if we use an apparatus with sharp directivity such as 3.3°in the half power beam angle, because the imaginary echo-trace which recorded by the broad one, are not recorded at sloped or steep bottoms. 3) The reliability of sounding was not influenced by the frequency of ultrasound in this experiment, but it may be necessary to give consideration to the roughness of the bottom shape or the grainitude of the materials when more precise study is needed. 4) The high frequency ultrasonic echo-sounder may be applied in future for navigation use, because such nltrasonic has other advantage that the attenuation in bubble layer is fairly little.