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<!-- DFIN New ActiveDisclosure (SM) XBRL Linkbase Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date :2023-03-15T10:53:15.8401+00:00 -->
<!-- Copyright (c) 2023 Donnelly Financial Solutions, Inc. All Rights Reserved. -->
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    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_NonPeoNeoAverageYearEndFairValueOfEquityAwardsGrantedDuringYearThatRemainedUnvested_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non Peo Neo Average Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested.</link:label>
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    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_NonPeoNeoAverageInclusionOfEquityValues_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Peo Neo Average Inclusion of Equity Values</link:label>
    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_NonPeoNeoAverageInclusionOfEquityValues_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non Peo Neo Average Inclusion of Equity Values.</link:label>
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    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_NonPeoNeoAverageExclusionOfChangeInPensionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non Peo Neo Average Exclusion of Change in Pension Value.</link:label>
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    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_RichardWKinzleyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Richard W. Kinzley</link:label>
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    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_ScottABuchholzMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Scott A. Buchholz</link:label>
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    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_NonPeoNeoAverageChangeInFairValueFromLastDayOfPriorYearToVestingDateOfUnvestedEquityAwardsThatVestedDuringYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Peo Neo Average Change in Fair Value from Last Day of Prior Year to Vesting Date of Unvested Equity Awards that Vested During Year</link:label>
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    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Central Index Key</link:label>
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    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_NonPeoNeoAverageChangeInFairValueFromLastDayOfPriorYearToLastDayOfYearOfUnvestedEquityAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non Peo Neo Average Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards.</link:label>
    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_NonPeoNeoAverageInclusionOfPensionServiceCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Peo Neo Average Inclusion of Pension Service Cost</link:label>
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    <link:label xml:lang="en-US" xlink:type="resource" xlink:label="bkh_BrianGIversonMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Brian G. Iverson</link:label>
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