At the hearing evidence shall be introduced in support of the petition and all interested parties may be heard for or against it. The court shall make findings and conclusions and enter an order granting or refusing the petition, and if the petition is granted, shall fix the water level to be maintained and direct the department of ecology to regulate and control the outflow of the lake so as to properly maintain the water level so far as practicable within maximum and minimum limits when the proper control devices are installed: PROVIDED, That the court shall have continuing jurisdiction after a petition is once granted and shall, upon subsequent petition filed and heard in accordance with the preceding sections, make such further findings and conclusions and enter such further orders as are necessary to accomplish fully the objectives sought in the initial petition: AND PROVIDED FURTHER, That shall the court find any such riparian owners abutting on a stream or river flowing from such lake be adversely affected in any way by the granting of such a petition, such petition shall be refused.