Spencer, J.
— Appellant is the owner of a certain dam and hydraulic generating plant constructed under the authority of §5081 Burns 1914, Ads 1907 p. 280, at the town of Williams, in Lawrence county. The dam is located in and across White river, a permanent stream or water course at that point, and by its construction the water in said stream was set back- and caused to overflow a part of appellee’s lands. To. appropriate the lands so overflowed and to assess the damages sustained by appellee through such appropriation is the purpose of this action. In prosecuting this appeal from a verdict and judgment fixing said damages, appellant alleges error of the court below in overruling its motion for a new trial and challenges specifically the admission and rejection of certain evidence and the refusal to give certain instructions requested by it.
1. *372. *36Over' appellant’s objection, two physicians were permitted to testify that in their opinion the overflowage from appellant’s ■ dam would increase the-breeding of mosquitoes along the river, and thus cause malaria among tenants on appellee’s farm. There is no objection to the admission of this evidence. Courts take judicial knowledge of the fact that overflows and floods *37are followed by disease and that swampy lands are detrimental to public health. Evidence of witnesses who are properly qualified to show the probable effect of such conditions on those living near is admissible. Applegate v. Franklin (1904), 109 Mo. App. 293, 305, 84 S. W. 347.
3. 4. Another class of evidence to which objection is made is illustrated by the examination of Nathan Freeman, witness for appellee. After testifying that he found the water in a well on appellee’s farm in bad condition, he was asked this question: “You may state now what caused the condition, if you can, that you found?” Over an objection that the witness was not sufficiently qualified and that the question called for a decision and opinion on a matter to be determined by the jury in view of all the evidence, the witness replied: “I believe the backwater from the dam.” No attempt was made to show that the witness was qualified to answer the questions propounded to him or to elicit the facts on which he based his opinion. On cross-examination he admitted that the well was on high ground, and that he did not know how deep it was or what relation existed between the level of the well and that of the water in the river. It is the law of this state, as announced in New Jersey, etc., R. Co. v. Tutt (1906), 168 Ind. 205, 216, 80 N. E. 420, 424, “that a witness will not be allowed to express an .opinion upon a subject of which the jury is as well prepared to judge as the witness; or, as generally expressed, he will not be permitted to give his opinion upon the exact question the jury are to decide.” This is especially true where it is clear that the witness is not qualified to express such opinion. Appellant’s objection to the question should have been sustained.
*385. Objection is also urged to. evidence introduced byappellee for the purpose of showing the value of his land before and after the construction of appellant’s dam. We need not consider these objections in detail, it being sufficient to say that when witnesses testify as to the fair and reasonable value of property taken in appropriation proceedings they should qualify themselves as having knowledge of the value of such property in the locality in which the same is situated. Muncie, etc., Traction Co. v. Citizens’ Gas, etc., Co. (1912), 179 Ind. 322, 100 N. E. 65.
6. After evidence had been introduced to show a depreciation in the value of appellee’s farm, appellant sought to prove by the tenant on the farm that appellee had increased his rent after the dam was constructed. This evidence was excluded. Where property has been flooded by reason of the lawful construction of a dam, ,the measure of damages is the value of the land permanently submerged, together with the depreciation in value of the remainder which is due to such construction. The rent agreed on between appellee and his tenant was a matter of private contract, and was collateral to the question at issue, namely, the actual value of the farm. Evidence as to such contract was irrelevant and therefore properly excluded.
The other questions presented will probably not arise on a second trial and it is unnecessary here to consider them. Judgment reversed, with instructions to sustain appellant’s motion for a new trial and for further proceedings not inconsistent herewith.
Note. — Reported in 111 N. E. 925. See 85 Am. St. 302; Ann. Cas. 1913A 1361.